Exposing and Using S-Log2 on the Sony A7s. Part One: Gamma and Exposure.

This guide is for the A7S and A7SII. The A7SIII does not in my opinion need the same degree of over exposure as documented here. So please bear this in mind if using the A7SIII.

This document has been prepared independently of Sony. It is based on my own findings having used the camera and tested various exposure levels and methods. Part 2 which explains how to use LUT’s to correct the footage in the edit suite or post production is here: https://www.xdcam-user.com/2014/10/using-s-log2-from-the-a7s-in-post-production/

If you find this useful please consider buying me a coffee or a beer. I’m not paid to write these articles.


pixel Exposing and Using S-Log2 on the Sony A7s. Part One: Gamma and Exposure.

One of the really nice features of the Sony A7s and Sony’s other Alpha cameras, including the A6300, A6500 etc is the ability to use different gamma curves and in particular the Sony S-Log2 gamma curve.

What are gamma curves?

All conventional cameras use gamma curves. The gamma curve is there to make the images captured easier to manage by making the file size smaller than it would be without a gamma curve. When TV was first developed the gamma curve in the camera made the signal small enough to be broadcast by a transmitter and then the gamma curve in the TV set (which is the inverse of the one in the camera) expanded the signal back to a normal viewing range. The current standard for broadcast TV is called “Recommendation BT-709”, often shortened to Rec-709. This gamma curve is based on standards developed over 60 years ago and camera technology has advanced a lot since then! Even so, almost every TV and monitor made today is made to the Rec-709 standard or something very similar. Many modern cameras can capture a brightness range, also known as dynamic range, that far exceed the Rec-709 standard.

The limitations of standard gammas.

As gamma effects the dark to light range of the image, it also effects the contrast of the image. Normal television gamma has a limited dynamic range (about 6 to 7 stops) and as a result also has a limited contrast range.

Normal-Gamma Exposing and Using S-Log2 on the Sony A7s. Part One: Gamma and Exposure.
When shooting a high contrast scene with conventional gamma the brightest highlights and the darkest shadows cannot be recorded. The contrast on the TV or monitor will however be correct as the camera captures the same contrast range as the monitor is able to display.

Normally the gamma curve used in the camera is designed to match the gamma curve used by the TV or monitor. This way the contrast range of the camera and the contrast range of the display will be matched. So the contrast on the TV screen will match the contrast of the scene being filmed and the picture will look “normal”. However the limited dynamic range may mean that very bright or very dark objects cannot be accurately reproduced as these may exceed the gammas dynamic range.

Slide5 Exposing and Using S-Log2 on the Sony A7s. Part One: Gamma and Exposure.
Although the dynamic range of Rec-709 may not always capture the entire range of the scene being shot, as the gamma of the camera matches the gamma of the TV the contrast will appear correct.

The over exposure typical of a restricted range gamma such as Rec-709  is commonly seen as bright clouds in the sky becoming white over exposed blobs or bright areas on faces becoming areas of flat white. Objects in shade or shadow areas of the scene are simply too dark to be seen. But between the overexposed areas and any under exposure the contrast looks natural and true to life.

Slog-709-FH Exposing and Using S-Log2 on the Sony A7s. Part One: Gamma and Exposure.
Typical limited Rec-709 exposure range. Contrast is good but the clouds are over exposed and look un-natural.

Log Gamma.

Log gamma, such as Sony’s S-Log2, allows the camera to capture a much greater brightness range or dynamic range than is possible when shooting with conventional television gamma. Dynamic range is the range from light to dark that the camera can capture or the range that the monitor or TV can display within one image. It is the range from the deepest blacks to the brightest whites that can be captured or shown at the same time.

There are some things that need to be considered before you get too excited about the possibility of capturing this much greater dynamic range. The primary one being that if the camera is set to S-log2 and the TV or monitor is a normal Rec-709 TV (as most are) then there is no way the TV can correctly display the image being captured, the TV just doesn’t have the range to show everything that the camera with it’s high range log gamma can capture accurately.

Fixed Recording Range For Both Standard and Log Gamma.

The signal range and signal levels used to record a video signal are normally described in percent. Where black is 0% and the brightest thing that can be recorded is normally recorded at 100% to 109%. Most modern video cameras actually record the brightest objects at 109%. The important thing to remember though is that the recording range is fixed. Even when you change gamma curve the camera is still constrained by the zero to 109% recording range. The recording range does not change whether you are recording Rec-709 or S-log2. So log gamma’s like S-Log2 must squeeze a much bigger signal range into the same recording range as used by conventional Rec-709 recordings.

Slide6 Exposing and Using S-Log2 on the Sony A7s. Part One: Gamma and Exposure.
Log gamma squeezes the scenes large range to fit in the camera’s normal 0%-109% recording range.

Recording S-Log2.

In order to record using S-log2 with the A7s you need to use a picture profile. The picture profiles give you several recording gamma options. For S-log2 you should use Picture Profile 7 which is already set up for S-log2 and S-Gamut by default (for information on gamuts see this article). In addition you should ALWAYS use the cameras native ISO which is 3200 ISO and it is normally preferable to use a preset white balance. Using any other ISO with S-log2 will not allow you to get the full benefit of the full 14 stops of dynamic range that S-log2 can deliver. In most of the Alpha cameras you now also have the ability to use a different version of S-log, – S-Log3 and this is found in picture profiles 8 and 9. You can use S-Log3 if you wish, but S-Log2 was designed from the outset by Sony to work with digital camera sensors. S-Log3 is based on an older curve designed for film transfers to a 10 bit recording. As a result when using a camera that only has 8 bit recording with a limited number of code values, S-Log2 tends to be more efficient and yield a better end result. This is what it was designed for.

Grey Cards and White Cards.

Before I go further let me introduce you to grey and white cards in case you have not come across them before. Don’t panic you don’t have to own one, although I would recommend getting a grey card such as the Lastolite EzyBalance if you don’t have one. But it is useful to understand what they are.

The 90% White Card.

The 90% white card is a card or chart that reflects 90% of the light falling on it. This will be a card that looks very similar in brightness to a piece of ordinary white paper, it should be pure white, some printer papers are bleached or coloured very slightly blue to make them appear “brilliant white”  (as you will see later in many cases it is possible to use an ordinary piece of white paper in place of a 90% white card for exposure).

The Grey Card.

The 18% grey card, also often called “middle grey” card, is a card that reflects 18% of the light falling on it. Obviously it will appear much darker than the white card. Visually to us humans an 18% grey card appears to be half way between white and black, hence it’s other name, “middle grey”.

Middle grey is important because the average brightness level of most typical scenes tends to be around the middle grey brightness value. Another key thing about middle grey is that because it falls in the middle of our exposure range it makes it a very handy reference level when measuring exposure as it is less likely to be effected by highlight compression than a 90% white card.

Exposing White and Middle Grey.

Coming back to Rec-709 and conventional TV’s and monitors. If we want a piece of white paper to look bright and white on a TV we would record it and then show it at somewhere around 85% to 95% of the screens full brightness range. This doesn’t leave much room for things brighter than a white piece of paper! Things like clouds in the sky, a shiny car, a bright window or a direct light source such as a lamp or other light.  In order to make it possible for S-log2 to record a much greater dynamic range the recording level for white and mid tones is shifted down. Instead of recording white at 85%-95%, when using S-log2 or S-Log3 it is recommended by Sony that white is recorded at around 60%. For S-Log2 Middle grey moves down too, instead of being recorded at 42%-43% (the normal level for Rec-709) it’s recorded at just 32% with S-Log2 (S-log3 uses 41%).

By recording everything white (ie a white piece of paper) and darker in a  lower range, we free up  lot of extra space above the white recording level, within the full recording range, to record all those bright highlights in any scene that would be impossible to record with conventional gammas where there is only 10% to 20% from white at 90% to the peak of the recording range at 100 to 109%.

Slide7 Exposing and Using S-Log2 on the Sony A7s. Part One: Gamma and Exposure.
To make room for the extra dynamic range and the ability to record very bright objects, white and mid tones are shifted down in level by the S-log2 gamma curve. As a result, white, mid tones etc will be displayed darker than normally expected with conventional gamma.

As S-Log2 and S-Log3 normally shift a lot of the recording levels downwards, if we show a scene shot with S-Log2 or S-log3 that has been exposed correctly on a conventional TV or monitor it will look dark due to the lower recording levels. In addition it will look flat with very low contrast as we are now squeezing a much bigger dynamic range into the limited conventional Rec-709 display range of a normal TV or computer monitor.

Slide8 Exposing and Using S-Log2 on the Sony A7s. Part One: Gamma and Exposure.
The on screen contrast appears reduced as the capture contrast is greater than the display contrast.

This on screen reduction in contrast and the darker levels are actually perfectly normal when shooting using log gamma, this is how it is supposed to look on a normal monitor or TV. So don’t be alarmed if when shooting using S-Log your images look a little darker and flatter than perhaps you are used to when shooting with a standard gamma. You will adjust the S-Log footage in post production to restore the brightness and contrast later.

S-log2-correct-FH-1024x576 Exposing and Using S-Log2 on the Sony A7s. Part One: Gamma and Exposure.
Correctly exposed S-Log2 can look dark and washed out.

The post production adjustment of S-Log2 and S-log3 is very important and one of the keys to getting the very best finished images. The S-Log recording acts as a digital negative and by “processing” this digital negative in post production (normally referred to as “grading”) we manipulate the large 14 stop dynamic range of the captured image to fit within the limited display range of a Rec-709 TV in a pleasing manner. This may mean pulling up the mid range a bit, pulling down the highlights and bit and generally shifting the brightness and colour levels of different parts of the image around  (see PART 2 for more post production information).

SLog-2 and 10 bit or 8 bit data.

Originally Slog-2 was designed for use on high end digital cinema cameras such as Sony’s F65 camera. These cameras have the ability to record using 10 bit data. A 10 bit recording can have up to around 1000 shades of grey from black to white. The A7s however uses 8 bit recording which only has a maximum of 235 shades from black to white. Normally 8 bit recording is perfectly OK as most transmission and display standards are also 8 bit. Shoot with an 8 bit camera and then display that image directly via an 8 bit system and nothing is lost. However when you start to grade and manipulate the image the difference between 8 bit and 10 bit becomes more significant. If you start to shift levels around, perhaps stretching out some parts of the image then the increased tonal resolution of a 10 bit recording helps maintain the very highest image quality. Photographers that have shot using both jpeg and raw will know how much more flexibility the 12 bit (or more) raw files have compared to the 8 bit jpeg’s. However they will also know that 8 bit jpeg’s can be also adjusted, provided you don’t need to make very large adjustments.

Contrary to popular belief heavy grading of 8 bit footage does not necessarily lead to banding in footage across smooth surfaces except in extreme cases. Banding is more commonly a result of compression artefacts such as macro blocking. This is especially common with very highly compressed codecs such as AVCHD. The 50Mbps XAVC-S codec used in the Sony Alpha cameras is a very good codec, far superior to AVCHD and as a result compression artefacts are significantly reduced, so banding will be less of an issue than with other lower quality codecs. If you’re going to shoot using S-Log2, some grading will be necessary and as we only have 8 bit recordings we must take care to expose our material in such a way as to minimise how far we will need to push and pull the material.

Getting Your Exposure Right.

When S-Log2 was developed the engineers at Sony produced tables that specified the correct exposure levels for s-Log2 which are:

exposure-table1 Exposing and Using S-Log2 on the Sony A7s. Part One: Gamma and Exposure.As you can see the nominal “correct” exposure for S-Log2 is a lot lower than the levels used for display on a typical Rec-709 TV or monitor. This is why correctly exposed s-log2 looks dark on a conventional TV. The implication of this is that when you grade your footage in post production you will have to shift the S-log2 levels up quite a long way. This may not be ideal with an 8 bit codec, so I decided to carefully test this to determine the optimum exposure level for the A7s.

Correct Exposure.

The panel of images below is from the A7s recording S-log2 and exposed at the Sony recommended “correct” 32% middle grey level. The correct exposure was determined using a grey card and an external waveform monitor connected to the cameras HDMI output. Then the S-log2 was corrected in post production to normal Rec-709 levels using a Look Up Table (LUT – more on LUT’s in part 2). You can also see the viewfinder display from the camera. If you click on the image below you can expand it to full size. Sorry about the shadow from the laundry line, I didn’t see this when I was shooting the test shots!

Slog2-correct-exposure-panel-1024x564 Exposing and Using S-Log2 on the Sony A7s. Part One: Gamma and Exposure.
Correctly exposed S-Log2 from A7s.

From this you can see just how dark and low contrast looking the original correctly exposed S-log2 is and how much more vibrant the corrected Rec-709 image is. I have also indicated where on the cameras histogram middle grey and white are. Note how much space there is to the right of white on the histogram. This is where the extra highlight or over exposure range of S-log2 can be recorded. When correctly exposed S-log2 has an exposure range of 6 stops above middle grey and 8 stops under.

Over Exposing or “Pushing” S-log2.

If we deliberately raise the exposure level above the Sony recommended levels (known as pushing the exposure), assuming you grade the image to the same final levels some interesting things happen.

For each stop we raise the exposure level you will have 1 stop (which is the same as 6db) less noise. So the final images will have half as much noise for each stop up you go. This is a result of exposing the image brighter and as a result not needing to raise the levels in post as far as you would if exposed at the normal level.

You will loose one stop of over exposure headroom, but gain one stop of under exposure headroom.

Bright highlights will be moved upwards into the most compressed part of the log gamma curve. This can result in a loss of texture in highlights.

Skin tones and mid tones move closer to normal Rec-709 levels, so less manipulation is need for this part of the image in post production.

This last point is important for the A7s with it’s 8 bit codec, so this is the area I looked at most closely. What happens to skin tones and textures when we raise the exposure?

Exposing at +1, +2 and +3 Stops.

Below are another 3 panels from the A7s, shot at +1 stop, +2 stops and +3 stops. Again you can click on the images if you wish to view them full size.

Slog2-plus1-exposure-panel-1024x564 Exposing and Using S-Log2 on the Sony A7s. Part One: Gamma and Exposure.
A7s S-Log2 over exposed by one stop.
Slog2-plus2-exposure-panel-1024x564 Exposing and Using S-Log2 on the Sony A7s. Part One: Gamma and Exposure.
A7s S-Log2 over exposed by 2 stops.
Slog2-plus3-exposure-panel-1024x564 Exposing and Using S-Log2 on the Sony A7s. Part One: Gamma and Exposure.
A7s S-Log2 over exposed by 3 stops.

Looking at these results closely you can see that when you increase the exposure by 1 stop over the Sony specified correct level for S-log2 there is a very useful reduction in noise, not that the A7s is particularly noisy to start with, but you do get a noticeably cleaner image.

Below are 4 crops from the same images, after grading. I really recommend you view these images full size on a good quality monitor. Click on the image to view larger or full size.

A7s-over-exposure Exposing and Using S-Log2 on the Sony A7s. Part One: Gamma and Exposure.
Crops at different exposure of LUT corrected A7s S-log2 footage.

The noise reduction at higher exposures compared to the base exposure is very clear to see if you look at the black edge of the colour checker chart (the coloured squares), although the difference between +2 and +3 stops is very small. You can also see further into the shadows in the +3 stop image compared to the base exposure. A more subtle but important effect is that as the exposure goes up the visible texture of the wooden clothes peg decreases. The grain can be clearly seen at the base level but by +3 stops it has vanished. This is caused by the highlights creeping into the more compressed part of the log gamma curve. The same thing is happening to the skin tones in the +3 stop image, there is some reduction of the most subtle textures.

From this we can see that for mid tones and skin tones you can afford to expose between 1 and 2 stops above the Sony recommended base level. More than 2 stops over and brighter skin tones and any other brighter textures start to be lost. The noise reduction gain by shooting between one and 2 stops over is certainly beneficial. The down side to this though is that we are reducing the over amount of exposure headroom.

Slide02 Exposing and Using S-Log2 on the Sony A7s. Part One: Gamma and Exposure.
As you raise the exposure level you reduce the over exposure headroom.

Given everything I have seen with this 8 bit and almost every other 8 bit camera my recommendation is to shoot between the Sony recommended base S-log2 level and up to two stops over this level. I would try to avoid shooting more than 2 stops over as this is where you will start to see some loss of texture in brighter skin tones and brighter textures.  Exactly where you set your exposure will depend on the highlights in the scene. If you are shooting a very bright scene you will possibly need to shoot at the Sony recommended level to get the very best over exposure headroom. If you are able to expose higher without significantly compromising any highlights then you should aim to be up to 2 stops over base. But whatever you do never expose darker than the Sony base level, this will normally look really nasty.

Determining The Correct Exposure.

The challenge of course is determining where your exposure actually is. Fortunately as we have seen, provided you in the right ball park, S-log2 is quite forgiving, so if you are a little bit over exposed it’s probably not going to hurt your images much. If you have a waveform monitor then you can use that to set your exposure according to the table below. If you don’t have proper white or grey cards you can use a piece of normal white paper. Although slightly less accurate this will get you very close to where you want to be. Do note that white paper tends to be a little brighter than a dedicated 90% reflectivity white card. If you don’t have any white paper then you can use skin tones, again a bit less accurate but you should end up in the right zone.

A7s-exposure-levels-1024x358 Exposing and Using S-Log2 on the Sony A7s. Part One: Gamma and Exposure.
My suggested exposure levels for the Sony A7s. The “sweet spot” is from normal to +2 over.

If you don’t have an external waveform monitor then you do still have some good options. Sadly although the camera does have zebras, these are not terribly useful for S-log2 as the lowest the zebras can go is 70%.

Light Meter: You could use a conventional photography light meter. If you do choose to use a light meter I would recommend checking the calibration of the light meter against the camera first.

Mark 1 Eyeball: You could simply eyeball the exposure looking at the viewfinder or rear screen but this is tricky when the image is very flat.

In Camera Metering: The cameras built in metering system, like the majority of DSLR’s is calibrated for middle grey. By default the camera uses multi-point metering to measure the average brightness of several points across the scene to determine the scenes average brightness and from there set the correct base S-log2 exposure.

Auto Exposure:

When you are using S-Log2, auto exposure in most cases will be very close to the correct base exposure if you use the default Multi-Zone exposure metering. The camera will take an average exposure reading for the scene and automatically adjust the exposure to the Sony recommended 32% middle grey exposure level based on this average. In the P, A and S modes you can then use the exposure compensation dial to offset the exposure should you wish. My recommendation would be to add +1 or +2 stops via the dial. Then observe the histogram to ensure that you don’t have any significant over exposure. If you do then reduce the exposure compensation. Lots of peaks to the far right of the histogram is an indication of over exposure.

Manual Exposure And Internal Metering.

If you are exposing manually you will see a small M.M. indication at the bottom of the LCD display with a +/- number. In the eyepiece viewfinder this appears as a scale that runs from -5 to +5, in S-log2 only the -2 to +2 part of the scale is used. In both cases this is how far the camera thinks you are away from the optimum exposure. + meaning the camera is over exposed, – meaning under.

A7s-VF-MM Exposing and Using S-Log2 on the Sony A7s. Part One: Gamma and Exposure.
A7s Viewfinder indications in manual exposure mode showing both M.M. offset from metered exposure and histogram.

In the image above we can see the M.M. indication is +0.3, in the eyepiece you would see a small arrow one bar to the right of “0” , indicating the cameras multi zone metering thinks the shot is just a little over exposed, even though the shot has been carefully exposed using a grey card and external waveform monitor. This error is probably due to the large amount of white in the shot, white shirt, white card, test charts with a lot of brighter than grey shades.  In practice an error of 0.3 of a stop is not going to cause any real issues, so even if this was exposed by setting  the exposure so that you have “M.M. 0.0” the exposure would be accurate enough. But it shows that multi point exposure averaging is easily confused.

The scene above is a fairly normal scene, not excessively bright, not particularly dark. If shooting a snow scene for example the cameras multi point averaging would almost certainly result in an under exposed shot as the camera attempts to bring the bright snow in the scene down to the average middle grey level. If shooting a well lit face against a very dark background then the averaging might try to bring the background up and the shot may end up overexposed.

If you want really accurate exposure then you should put the cameras metering system into the spot metering mode where instead of taking an average of various points across the scene the camera will just measure the exposure at the very center of the image.

spot-metering-mode Exposing and Using S-Log2 on the Sony A7s. Part One: Gamma and Exposure.
A7s Spot Metering Mode.

You can then use a grey card to very accurately set the exposure. Simply place the circular shaped symbol at the center of the viewfinder display over a grey card and set the exposure so that M.M is 0.0 for the correct S-Log2 base exposure. To expose 1 stop over with a grey card, set M.M. +1.0 and two stops over M.M. +2.0 (not flashing, flashing indicates more than +2 stops).

MM-00-grey Exposing and Using S-Log2 on the Sony A7s. Part One: Gamma and Exposure.
Using Spot Metering to set exposure correctly for S-log2. MM 0.0.

One small issue with this is that the camera will only display a M.M. range of -2.0 to +2.0 stops. Provided you don’t want to go more than 2 stops over base then you will be fine with a grey card.

Using White Instead of Grey:

If you don’t have a grey card then you can use a 90% reflectivity white target. As white is 2 stops brighter than middle grey when S-Log2 is correctly exposed the 90% white should indicate M.M +2.0.

MM-plus2-white Exposing and Using S-Log2 on the Sony A7s. Part One: Gamma and Exposure.
Using spot metering to set the correct exposure for S-Log2. M.M should read M.M +2.0 for a 90% reflectivity white target.

Once you have established the correct exposure you can then open the iris by 1 or two stops to increase the exposure. Or halve the shutter speed to gain a one stop brighter exposure. Each time you halve the shutter speed your exposure becomes one stop brighter, so divide the shutter speed by 4 to gain a 2 stop increase in exposure. As always you should observe the histogram to check for any over exposure. White peaks at the far right of the histogram or disappearing completely off the right of the histogram is an indication of over-exposure. In this case reduce your exposure back down towards the base exposure level (M.M 0.0 with a a grey card).

Exposure Summary:

I recommend using an exposure between the “correct” base S-Log2 exposure level of middle grey at 32% and two stops over this. I would not recommend going more than 2 stops over over base.

In the P, A and S auto exposure modes, when using the default multi-zone metering the camera will set the base S-log2 exposure based on the average scene brightness. For most typical scenes this average should be very close to middle grey. This exposure can then be increased (brightened) by up to 2 stops using the exposure compensation dial.

In manual exposure the “M.M.” number displayed at the bottom of the viewfinder display is how far you are from the correct base S-log2 exposure. M.M. +2.0 indicates +2 stops over base. If using multi zone metering (the cameras default) this exposure will be based on the scenes average brightness.

If you set the metering to “Spot” you can use a grey card centred in the image to determine the correct base exposure and up to 2 stops of over exposure via the M.M. indication when shooting manually.

In Part 2:

In part two I will take a look at grading the S-log2 from the A7s and how to get the very best from the S-log2 images by using Look Up Tables (LUT’s).

PART 2 – How to handle the footage in post production is here.

NORTHERN LIGHTS Tours and workshops.

Don’t forget I run storm chasing and Northern Lights expeditions every year.  These are amazing expeditions by snowmobile up on to the Finnmarksvidda. We go ice fishing, dog sledding, exploring, cook a meal in a tent and enjoy traditional Norwegian saunas.

More information here.

sky-full-of-Aurora-1024x683 Exposing and Using S-Log2 on the Sony A7s. Part One: Gamma and Exposure.
Northern Lights over our cabins in Norway.

228 thoughts on “Exposing and Using S-Log2 on the Sony A7s. Part One: Gamma and Exposure.”

  1. What a great tutorial!

    I have found +3 stops over middle to be great, especially in tandem with a Zebra of 100. I’m glad to see that it tops at 94 IRE at 90% white. Also, the sensor is capable of full swing all the way to 100+ IRE (assuming 109 IRE) so I think this method works great for S-Log2.

    So far, my observation as been that +3 stops is safe. Further testing is necessary, though.

    Thank you once again for an excellent tutorial.

  2. At +3 stops your really pushing things. Skin tones will be recorded slightly higher and using a narrower range than for normal Rec-709. Each stop of 8 bit S-Log2 only has around 25 shades per stop once you go above middle grey (Rec-709 has around 35-40 shades in the normal skin tone range). Each stop you go up in exposure the actual scene has double the brightness range of the previous. So with the limited 8 bit data when you start over exposing skin tones and then pulling them down in the grade you start reducing your effective tonal range. You can see this in the test shots.

    As the main noise reduction benefit occurs at +1 stop, is less of a benefit at +2 stops and really of almost no benefit at all at +3 stops there is no reason or benefit that I can see from shooting 3 stops over. You are reducing your tonal resolution in mid and skin tones, reducing your over exposure headroom to near 709 levels for no obvious gain over shooting at 2 stops over.

    At +2 stops the skin tone shift in post production when going to Rec-709 is at it’s smallest so this is where you should see the best skin tones from the 8 bit recordings. Darker skin tones and mid tones will have the smallest shift at +1 stop, so I believe the sweet spot is between +1 and +2 stops, depending on the highlight range of the scene you are shooting.

  3. Are you sure about your over/under numbers? My understanding is ‘correct’ is closer to +7/-7. Cine4 is known to have about 5.3 stops over and slog2 has a rated ISO about 1-2/3 stops over cine4, giving it that much more overexposure.

    1. Absolutely sure. S-Log2 Base gives +6 stops over and 8 stops under. If the values were incorrect then the LUT’s wouldn’t work, plus the information can be found from any S-log2 plot in any Sony published S-log2 or S-log3 white paper.

  4. Thanks for a very useful article. I’ve been very impressed by the footage I’ve seen from this camera around the web. Flat/Log profiles have been around for a long time for 8 bit cameras. There is plethora of them available for the 5d3. Why is slog2 on the Sony better than the various log gammas available for other 8 bit cameras?

    1. Because it’s a real log profile, not some half baked black gamma/knee affair that often doesn’t truly tap into the sensors full output range.

  5. Awesome article, Alister! Very helpful, since I just got the A7s and am trying to learn its capabilities. One question about shutter speed, I see in your outdoor shots it is 1/6400, while indoors 1/125. I thought one aims for a shutter speed double the frame rate? Or is there some other factor?
    Thanks, looking forward to part 2.

    1. doubling the frame rate is about the minimal frame rate to avoid flickering or ghosting for video. These were just pictures.

    2. I ended up with those shutter speeds as that allowed me to start at f16 for the exposure range tests. So I could go to f22 and to f5.6 or even f4. I wouldn’t use 1/6400 normally, but the camera is so damn sensitive. Waiting for my 10 stop ND’s to arrive.

  6. Thanks, Alister. You also mention time-lapse in one of your articles about the A7s, but I didn’t see it in the menus. Did you download a PlayMemories app, or some other way?

  7. Awesome article!
    Love ya work…
    I am experimenting cutting between my fs700 with slog2 and my a7s with slog 2
    Would all the info above also apply to an fs700?
    Thanks again

    1. Yes, I have been testing the same thing on the FS700 and my findings are the same. The LUT’s work with the FS700 too.

  8. Hi Alister, GREAT Articel ! This is what alot of us have been waiting for. Your invited to a coffee m8t ;).

    Just so I get this clear. If I go for a +2 overexposure and set my Zebra to 70% I should be fine regarding in correct exposure on Faces right ? Since I come from an ENG Background I am very used to shooting with Zebra set to 70%. This would make my life much easier finding the right exposure with the A7S.

    Cheers Gil.

    1. Yes you should be OK, but your zebras should only be on the darker skin tones. Then ideally you want to use one of my LUT’s in post to restore the correct levels as part of the grading process. This will be covered in part 2.

  9. Enjoy ur Coffee 😉 Do you think you can make an Article on the different Color Modes inside the S-Log2 Profile and what differences they make ? (S-Gamut, Cinema, Pro, ITU709,…) Really enjoyed ur Article. Keep up the good work !

    1. Thanks for the coffee!

      I’ll probably end up writing a whole series of articles on the A7s covering all the different gamma and colour space options. But it takes a lot of time, so it may be a little while before they are all done.There is an article on colourspace here: https://www.xdcam-user.com/2014/05/what-is-a-gamut-or-color-space-and-why-do-i-need-to-know-about-it/
      Although written for the F5/F55 the principles are exactly the same for the A7s.

  10. Thx. Ill have a look into it. Totaly understand that these things take alot of time ! No Pressure here 🙂

  11. Thanks mate!
    One sorta weird nooby question-is there anything in your exposure and camera setup ‘ritual’ that is different using the fs700 and the a7s in s-log2?
    Do you do white balance before exposure? same for different frame rates etc etc….any tips for setup with this combo?

    1. No not really. FS700 and A7s both behave the same.
      White balance depends on your post workflow. If you are going to use LUT’s (recommended) you should use preset white at either 5600 or 2300 (sunshine or tungsten).

  12. Geez your a good bloke!
    One coffee coming your way…
    A couple of other questions though-what did you do about ND? Any advice on this front?
    And do you know of any good guides on shooting sony slog2 in the more general sense? Want to try and learn all I possibly can…

  13. Lots to say here…

    First, the a7S’s S-Log2 gamma using S-Gamut color is very accurate against Sony’s ACES input device transform (the same one for the F65). After transformation into the ACES color space, the image is highly linear, and you can do exposure compensation over a range of many stops with nearly perfect results. Here’s a little test I did that shows it: http://www.youtube.com/watch?v=41grTkW4lUs If you want to really understand what the camera’s sensor is capturing and not be confounded by the peculiarities of S-Log2, transforming into ACES is the way to do it.

    Second, the S-Log2 gamma uses more codes per stop towards higher stops, not less. Here’s a chart that shows it nicely: http://community.sony.com/t5/F5-F55/S-Log3-vs-S-Log2/m-p/286167#M12596 So if you are properly transforming the S-Log2 levels to linear, there’s absolutely nothing to lose by exposing higher, so long as you don’t start to clip in the red, green, or blue channels in a way that the clipping would show up in your final rendered output. I’ve verified this with testing. Higher exposures are absolutely better, with less noise and less banding right up until clipping starts, and even then the only problem is the clipping in the clipped areas. Skin tones and color accuracy do not suffer with higher exposures. If anything they are slightly better. +3.0 on the exposure meter (if it actually went that high) is great, and clipping that would show up in the rendered output (after exposure compensation in ACES) starts somewhere beyond +3.0 most of the time. As a rule I try to expose between +2.0 and +3.0. +3.0 has a noticeable improvement in noise performance over +2.0, but I’m really not sweating the small amount of noise at +2.0 or even +1.0. This camera is really great for how I can vary the exposure over a wide range and still get great results after performing exposure compensation in ACES.

    If you’re not using ACES, then you are using a LUT or some RGB level mapping that is very particular for how the image is exposed, and a higher exposure won’t necessarily be better. There’s really only one correct exposure if you’re not using ACES, and this is probably what you’re seeing when you say that skin tones suffer at higher exposures. It’s not a limitation of the captured image. It’s a limitation of the way you are processing the video. Every LUT that maps the recorded image to some display-referred color space like BT.709 expects a certain exposure as input. The BT.709 color space is not linear and thus not a good space for performing exposure compensation, nor is S-Log2. To do exposure compensation correctly, it must be done in the linear domain. S-Log2 itself is a weird curve that is more akin to an extended BT.709 gamma curve than to a true log curve. When selectively mapping S-Log2 RGB levels into BT.709 levels, you’ll get very different results depending on how the image was exposed and thus on which range you need to select. You have some leeway here, but really only one exposure will be best, and still not as good as when using ACES or when recording directly to BT.709 with a correct exposure.

    Let me say it again: when you are not using ACES, there is only one correct exposure, and higher is not necessarily better. The correct exposure depends on which LUT (or level mapping scheme) you are using. It’s a limitation of your LUT, not of the camera’s recorded image.

    Picture Profile 7 defaults to S-Log2 gamma and S-Gamut color. These are the correct settings if you use the ACES S-Log2 IDT or another Sony-provided LUT intended for S-Log2. But it is the wrong color space if you are selectively mapping a range of S-Log2 RGB levels to BT.709 levels. That’s because S-Gamut is shifted in CIE xy space relative to BT.709’s gamut, and you cannot correct such a shifting with standard color correction tools. Such shifting requires a LUT, or a matrix acting on linear values. So if you are trying to use standard color correction tools to convert S-Log2 to BT.709, you should shoot with S-Log2 gamma and BT.709 color, not S-Gamut color. The picture profile should be customized to change the color mode to something other than S-Gamut.

    In S-Log2, ISO 3200 is not always preferable. We all know that higher ISOs are better, and I’ve told you that exposing higher is better for S-Log2. So what do you do when your exposure is maximized but the image is still too dark at ISO 3200? Do you leave the image in a middle or lower part of the S-Log2 range, or do you increase the ISO setting to shift the exposure into a higher part of the S-Log2 range? Noise performance and dynamic range will be the same either way, but you may face banding, especially in the shadows, if you don’t boost the ISO. That’s because S-Log2 has fewer level codes per stop at lower stops, and being just 8 bits on the S-Log2, the number of codes available in lower stops is pretty small. Of course if you can boost the exposure to expose into the upper part of the S-Log2 range AND keep an ISO setting of 3200, that’s best. But if your exposure is already maxed out, exposing into the upper part of the S-Log2 range is more important than keeping the ISO setting low. Boost the ISO as necessary to expose into the upper part of the S-Log2 range.

    Finally, a note about zebras. Zebras show the level of the output Y-channel (luma). On the a7S, a zebra setting of 100 corresponds to 100% luma in the output, and 100+ corresponds to a luma greater than 100% in the output. But that’s not the max luma value for S-Log2: S-Log2 goes up to 109%. So you have about one stop of additional highlight range above where zebras at 100+ start to show. But don’t forget that you can clip in the R, G, or B channel and not clip the Y (luma) channel. Looking at zebras is good for making sure that you don’t clip on a sunlit white object, but it won’t help so much to make sure you aren’t clipping in one or two channels of R, G, or B on saturated colors and skin tones.

    1. First of all, as stated in the article, LUT’s were used to do the transformations. There is a link at the head of the article to download the LUT’s and these LUT’s incorporate exposure compensation for both gamma and gamut. Included in the set are +1, +2 and +3 stop LUT’s, but it’s easy enough to produce LUT’s for +4 stops or whatever compensation you need. Using these LUT’s to correctly transform the S-log2/S-gamut to Rec-709 will be covered in part 2.

      Yes, of course you could use ACES, but I doubt that many of my readers are using ACES with the A7s. Those that know ACES probably won’t need to read the article.

      Of course you can expose at different levels when not using ACES. All you need is the correct LUT.

      Yes you are correct that in terms of actual bits used, S-log2 uses more or less the same number of bits per stop for the higher stops. But you appear to be ignoring the fact that each time you go up a stop in exposure, each time you open the iris one stop or light the scene one stop brighter you are doubling the amount of light falling on the sensor, doubling the contrast range. So open the iris an extra stop and the contrast range doubles, but the amount of data being used to record that only increases by a constant amount. For the scene to be recorded accurately you would have to double the amount of data being used, but this is not happening, the data is only increasing by a small amount, so you have less data per stop relative to the scene you are shooting. So over expose to the point where you are shifting levels down in range in post and you will be sacrificing information about the scene.

      If log really did offer the ability to over expose as much as you want without any consequence then there would be no need for linear recording or linear transforms. Why do you think that most log cameras are at least 10bit or better still 12 bit? The extra bits provide the buffer needed to allow for the lossy nature of log, but with the A7s we don’t have that luxury.

      Using a higher ISO than 3200 will reduce your dynamic range as the clipping/saturation point of the sensor is mapped to the top of the S-log2 gamma curve. Raise the gain and you will push this clipping point beyond what can be recorded so you can never take full advantage of the full range of the sensor. Any gain in the shadows is likely to be negligible as gain will also bring up the noise floor. If you are shooting a dark scene when dynamic range is not an issue, then yes you could raise the ISO, but you could also add gain in post. Either way you will bring up the noise as much as the signal. It is MUCH better to alter the exposure by adding light or opening the aperture rather than altering the gain/ISO of the camera. If you are shooting in such a dark environment that you feel there is the need to add gain, then frankly you don’t want to be using S-log2, you would be much better off using a narrower range gamma with even more bits per stop than S-log2, possibly Rec-709 will give you a better result.

      The primary reason for shooting with S-log2 is to gain a greater dynamic range.

  14. In your article you didn’t say which LUT you used. It is pointless to talk about the optimal exposure if you don’t say which LUT.

    I really don’t understand what you are saying about contrast. Contrast is relative brightness. If you increase the exposure by 1 stop, the bright parts become twice as bright and the dark parts become twice as bright. The contrast is unchanged. It doesn’t require any more data to record that image.

    S-Log2 has progressively more levels per stop at higher stops, not about the same. You don’t lose a thing by exposing higher. You gain, actually, until it clips.

    Log color spaces have more bits per sample so they can capture a large dynamic range without banding. It’s got nothing to do with any “lossy nature” of log. In fact a logarithmic scale is the optimal scale for encoding brightness levels, since human perception of brightness is logarithmic. A logarithmic scale makes best use of the limited number of codes available in an 8-bit or 10-bit or however many bit sample, regardless of the size of the dynamic range to be recorded.

    Raising the ISO reduces the dynamic range because the shadows become noisier, not whatever you said. Of course it’s better to add light than to increase the ISO setting. But if adding light is not an option, increasing the ISO setting shifts the image into a higher part of the S-Log2 curve that has more precision, reducing banding (especially in the shadows). Naturally it doesn’t help the noise performance and you still need to be careful of clipping.

    1. You are completely missing the point that while we perceive the world in a log way, a camera sensor does not and when you start manipulating levels, if you have not started off with an accurate representation of what the scene TRUELY looks like you will loose picture information. Log is perceptually lossless when you capture a scene 1:1 as the highlight roll off or effective data reduction (relative to true scene linear) mimics the way we perceive the world. But when you start raising those levels artificially so you can then reduce them later this no longer holds true.

      If you really don’t think that changing aperture (or changing the amount of light in a scene, pretty much the same effect) doesn’t have an effect on dynamic range then you need to go back to photography 101. Of course both bright and dark objects get brighter if you open the aperture or add light. But in addition you will see further into the shadows as objects previously in the noise floor become visible. Open the aperture and Black will still be black, brighter objects become brighter, the gap between black and brightest expands, contrast increases as the brightest objects become brighter relative to the darkest. Do you not see this change in contrast on your monitor when you open and close the aperture?
      According to your argument, that opening the aperture makes no difference to contrast or dynamic range, why do we even need cameras that can deal with big ranges? If a scene is too bright why not just stop down and close the aperture to deal with it? After all, according to you the dynamic range will be the same, according to you, exposure makes no difference to contrast range???? Obviously this is NOT the case. We all know that when trying to deal with a bright scene closing the aperture will reduce the brightness but also decrease the dynamic range as the low key parts of the shot are lost or squashed into the shadows where they can no longer be seen. And of course the opposite is equally true, opening the aperture increases the dynamic range and every time you open up by a stop you DOUBLE the dynamic range, a 100% increase, meanwhile the data increases by only around 10% if we are talking of the top 4 stops of S-Log2. I don’t understand why this is so hard to understand.

      Go up one stop the scene range doubles, data increases by only approx 10%.
      +1 stop = 100% recorded with just 10% more data.
      +2 stops = 200% recorded with just 20% more data.
      +3 stops = 400% recorded with just 30% more data.
      +4 stops = 800% recorded with just 40% more data…………………

      And you don’t think log is “lossy”????????? This is why there is a night and day difference between how much you can manipulate linear footage and log footage in post.

      Of course there is every point in talking about exposure without stating which LUT is used because the LUT does NOT effect your exposure. Even if you over expose by a couple of stops and then use a LUT without exposure compensation to convert to your chosen gamut you can still correct your exposure in post. The whole S-Gamut primaries shift is a red herring as once you have applied your LUT you are no longer using those skewed primaries, you will now be in your new colour space. It may not be quite as easy to grade an over exposed shot after converting with a base exposure LUT, but it is still absolutely possible. Your whole notion of ACES having only one single usable correct exposure is totally flawed because the whole point of ACES is to move everything into linear space where it doesn’t matter where your exposure is as everything is allocated the appropriate amount of data for the brightness captured. Take over exposed S-Log and convert it to ACES and EVERYTHING you have exposed is converted to linear, with the same correct transform for the colour space, from black to white. Once you are in that linear space you can easily reduce the gain to get your desired output levels. You don’t need a different IDT for every exposure level, the transform from gamma/gamut to linear is exactly the same in every case the ONLY difference is the output level which can very easily be adjusted in the ACES linear domain.

      The maximum dynamic range of a camera is determined in most cases by two things. One: The sensor noise floor and Two: The sensors saturation or clip point. When you add or remove gain these do not change, they are ALWAYS the same. In addition signal to noise ratio of the sensor remains fixed. Gain does not alter ratios, only levels.

      With something like S-log2 the darkest thing that can be meaningfully pulled out of the sensor noise floor is mapped to the bottom of the log curve and the brightest thing or the saturation point of the sensor is mapped to the top end (109%) of the curve. This is how you transfer the maximum dynamic range from the sensor to the recording.

      When you raise the gain/ISO BOTH the noise and smallest signals are amplified by the same amount and thus recorded at a brighter level. But you don’t gain any picture information as how far you can see into the shadows is limited by the sensor noise floor. You can’t suddenly see below the sensor noise floor. The signal to noise ratio does not change so there is no change to the dynamic range in the shadows, the amount of picture, relative to noise is EXACTLY the same. The ONLY change is in recording level. Brightness will increase, but we don’t see anything extra due to the matching increase in noise level. Do not confuse a brightness change with a dynamic range change.

      When you raise the gain any signal coming off the sensor at or close to the saturation point is amplified. So, what was recorded previously at 109% now goes higher than 109% and can no longer be recorded as it is beyond the recording range of the log curve, so you LOOSE the ability to record highlights that the sensor is actually capable of capturing because the gain makes the total signal range larger than can be recorded by the gamma curve. For every 6db you raise the gain you will loose 6db (or 1 stop) from the TOP of your recording range because you push what was previously at 109% beyond 109%.

      See: https://www.xdcam-user.com/2013/12/why-gain-is-bad-for-your-dynamic-range/
      Also: http://provideocoalition.com/aadams/story/no_pain_no_gain/

      This is why EVERY wide dynamic range video camera that I know of uses a fixed gain/ISO figure when capturing the widest possible dynamic range. This is why Arri/Red/F55 etc use exposure indexing to alter exposure mid point and NOT a shift in gain applied to the recording.

      If you are shooting in low light and you add gain to the recording to boost the brightness, most of the benefit of adding gain to supposedly raise the recording into a fatter (more data) part of S-Log2 curve is lost because you must remember that gain not only raises levels but expands them. If lets say the darkest signal is at 20mV and the brightest at 100mV at 0db gain then that’s an 80mV swing to be recorded. Add 6db of gain (x2) and those signals become 40mV and 200mV, so now the swing is 160mV, the swing has also doubled. So to record this we will need twice as many bits. Shifting the levels up the curve will give you more bits, but not double, The net result is that adding gain gives very little, if any benefit to quality of the recording.

      In a low light scenario where you feel gain is necessary it is so much better to use a different gamma curve more suited to this kind of scene, you would be crazy to use S-log2 unless you really need the dynamic range, in which case adding gain would undermine the whole reason for using S-log2.

      1. Wow you spreading gross misinformation. You are absolutely wrong if you think stopping up or down changes the absolute scene contrast (dynamic range) that falls on the sensor. I understand what you’re saying about the noise floor but by opening up and bringing tonal ranges above its threshold you are only talking about increasing the range to meet subjective judgements about acceptable noise levels. This does not have any effect on the absolute range of light that is falling on the sensor or that the sensor is recording. I think you are tripping up in your thought process about there being black tones that stay black no matter how much you open up. Truly black body object only exist in theory and in black holes. There isn’t a black substance on earth that you can put in front of a camera that won’t double in luminosity when you open a stop.

        “opening the aperture increases the dynamic range and every time you open up by a stop you DOUBLE the dynamic range” Wow are you serious? So if I have a camera who’s sensor has a 7 stop dynamic range all I have to do is open a stop and I get a camera with a 14 stop dynamic range? Open 2 stops and I get a 28 stop dynamic range? Someone needs to tell all these hollywood types to stop buying 100k dollar cameras and just open up a stop or two.. I think you are misunderstanding something somewhere along the line, not so sure Jacob is the one that needs to go back to photography 101 class.

        1. I never once state that the dynamic range of the sensor changes or that the dynamic range of the scene changes, I think you need to re-read the article, I’m not sure which one you are actually referring to, but I am well aware that a sensors DR does not change and that the DR of the scene does not change.

          But, yes if you open the aperture the dynamic range that the sensor can see can increase. Lets say the the noise floor of the camera is at 4%, so anything below 4% cannot be differentiated between noise and real signal. Lets say the brightest thing falling on the sensor is coming in at 60% and lets imagine that we have 6 stops between 4% and 60%.

          Now we open the aperture by 1 stop.

          Our 4% signal now becomes say 8% (depends on gamma curve etc) and our 60% signal becomes 90%.

          So what has happened here? The dynamic range recorded has increased. Not much has changed at the bright end, just an increase in level, but at the shadow end we can now see objects darker than we could before, so we are recording a greater dynamic range. The sensor/cameras maximum dynamic range has not changed and once the bright signal reaches the peak recording limit we will no longer gain any further recorded dynamic range, but until we reach that peak, opening the aperture will allow a greater dynamic range to be recorded.

    1. Hmmm, not sure, looks good on the surface, but I don’t know how the base dynamic range etc is established as the numbers are all wrong. Sony’s Cinegammas are 460% curves (11.5 stop) so they cannot record more DR than than 11.5 stops, that’s impossible. S-log2 is a 14 stop curve. Middle grey is also placed at the wrong point in the S-Log2 curve (it should be +6 stops/ -8 stops) so I am very suspect of how the base exposure settings are bing established, including some of the ISO’s mentioned. Normally using negative gain is a really bad thing to do with any kind of high dynamic range log curve. I’d also like to know how the S-log2 was handled in post, because the DR difference between S-Log2 and Cine 4 is really quite big and I don’t understand why this has not been seen.

  15. Very interesting; any chance you could join one of those threads, or may I direct people here/quote your comment? (they’re aware of this article).

  16. A really wonderful tutorial. Informative, generous and genuinely useful for a number reasons. It really is a nice gesture to share this valuable knowledge. Thank you. This will make a difference to how I use my camera and shoot log. Do you want sugar in that coffee?

  17. Hey Alister,

    Just bought you a cocktail and wanted to say thank you for sharing all of your knowledge! I’ve been following your posts since I bought my ex-1 back in 2008-09 I’ve learned so much from you and I’m truly grateful! Enjoy your drink 🙂

  18. In 2008, Alister, you helped me a great deal with my new EX3.
    Now this very clear explanation of the Slog2 of my A7S is a huge help to me. I already used it as a B camera in a documentary for night shots and low light scenes using the 3200 ISO, and my editor is very pleased with the results. After reading this excellent article of yours, I will make a better use in the next projects. Thanks again Alistair for your precious knowledge sharing with the community of story tellers 🙂

  19. Thanks Alister, I left a tip. Now that I have A7s in hand, I think this may be the most helpful article written about the camera to date. Thanks for all your knowledge and generosity in sharing it.

    1. I have the Fotodiox E-Mount to EF mount with built in variable ND. Only works with manual mechanical lenses. No electronics.

  20. Excellent article – thank you very much for taking to time to write this and share it with the video community…very very much appreciated.

  21. Finally, I got the idea of Rec-709 and S-log2! Those were mysterious for me, and now everything is clear 😀
    I’m awaiting my Blackmagic Pocket camera, so this knowledge will come handy 🙂

  22. Hey, Alister. This is great info. I run a small biz making “family-story” videos for families and recently bought a Sony A7S to become my “A” camera–and your work here is wonderfully helpful. I hope you’ve enjoyed the cocktail I sent you a week ago. And I hope Part 2 is coming out very soon!
    Thanks again, Bill

  23. Thank Alister 😉
    I don’t know this integrated ND in the adapter.
    Is that good, especially for the sharpness ?
    Comparing for example with Tiffen, Singh-ray, Lee filter …..

  24. Hi Alister,
    Great great stuff by the way…found it hugely helpful in figuring out my new A7S…
    One doubt perhaps is how are you seeing a histogram there…I really can’t find histogram anywhere. I,ve always worked with histogram for most of my shooting and here really finding it difficult without it.

    Thank You.

  25. Thank you so much for explaining this Alister. This is the first article that I have read that explains it clearly. I really can’t wait to read part two!! Thanks again for posting this!

  26. Thanks for this really useful article. This approach makes a lot of sense and with the sensitivity of the camera works for almost all situations, but what about shooting in really low light/no light to take advantage of the higher ISO settings like 51200. Is S-log 2 still the best way to go or are other settings better when pushing things that far (or further)? Assuming a full grade of the footage…

    1. You will only ever get the full 14 stops of dynamic range at the native 3200 ISO. For every stop you go up or down in ISO you loose 1 stop of dynamic range. So if you went say to 12800 ISO there is little point in using S-Log2 as you will only have 12 stops of DR at most and the other gamma curves will probably give a better final result.

      1. Yes, you’ll get the “14 stops” of dynamic range if you exposure for middle grey at 0EV but if you expose for middle grey at +2EV (or close to it) as so many people do to combat noise in SLOG2 then your latitude in the highlights is cut by 2 stops. Because the way you are exposing is as though +2EV will actually be a 0EV reference within the zone system. So this will give you only about 4 stops of overexposure latitude before the highlights are clipped into 109 IRE. It would be more correct to say that A7s has 4 stops of overexposure latitude and 10 stops of underexposure latitude, especially in any situation involving actors aka skintones.
        Thus, for most situations the A7s and also the newer Sony mirrorless camera models, such as the a6500 and A7III, actually aren’t that good in highlight capture. Definitely a far cry from Arri Alexa territory!

        From my own experiments of latitude testing with the sony A7s and a6500 I generally clip highlights at around 3.3 stops above +2 EV for middle grey. In other words an unimpressive 3.3 stops of overexposure latitude. Not too far off lovely REC709 latitude. How depressing 🙁 Again assuming +2EV serves as a 0EV reference since that’s where you want your middle grey to be in order to get the best skintones.
        For landscape shots yes, you can expose middle grey lower (average metering often works ok) around +1EV as you’ve stated. All in all though, the assumption that the A7s has 6 stops of latitude above middle grey I consider extremely misleading. YES it does do “6 stops” (->5.3 in my testing-<) if you don't mind some ugly noise when exposing Middle Grey for 0EV, but NO it doesn't do "6 stops" if you expose for +2EV as a middle grey zone system equivalent. Inststead you'll get just 4 stops of latitude above middle grey (3.3 in my testing).

        I think using CINE4 is the best compromise on the sony mirrorless cams for most scenarios. Just underexpose by about a stop and push the levels back up in post. That will give you about 4.3 stops of exposure above middle grey latitude.

        By the way Alistair, thank you so much for all your great knowledge. I have watched many of your vids in the past and learnt a lot. Thank you! 🙂

        1. Wow, you are getting very poor log results compared to most people. Given that there is no change to the sensor between Cine 4 and S-log2 I am surprised to hear you say that using underexposed Cine 4 with a post push is giving you better results than similarly exposed S-Log2. After all the main determining factor for the final image noise will almost always be how much light you put on the sensor, so really there shouldn’t be any significant difference. Logs big benefit is the lack of highlight roll-off, so in post you are able to extract a lot more detail and texture from the highlights than you can from the cinegammas where the roll-off means that the last stop, although perhaps not clipped contains very little useable picture information.

  27. What an amazing valuable article on the Slog-2! Thank you very much for this and the LUT’s If you haven’t already shot Aurora with it, you’re going to love this camera for that purpose! Amazing results. Here is some of what I’ve shot with it so far this season

    as the dynamic range is difficult to capture any other way. Noise is still a bit heavier than I’d like as I’m already pushing the limits of the f/1.4 lens and frame rate so I’m having to push ISO a bit beyond my comfort zone on occasion but up to 40k it’s pretty clean. I did even mange to shoot some footage at 60fps and slow it down. Can’t wait to see what you do with this camera! Thanks for the info and I’ve purchased a cocktail for you! 😉

  28. This is an interesting perspective. For Northern Lights, where I need a little head room in the highlights when they get intense, I’ve found Slog to still give me the best results for pulling highlights back a bit and cleaning noise. Would you suggest another profile for Aurora at say 40k ISO?

    1. Once you go away from 3200 ISO you are not getting the cameras full dynamic range, so S-Log2 is wasted. You would be better off using one of the cinegammas.

  29. Hey Alister, first I want to say thank you for writing this long article. I’ll be donating to you very soon. I had a question. First, let me start off by saying I can do some basic grading, but this is my first using something like slog2 to pull in more color information and giving me a flat looking image to fix it later in post.

    I was wondering why I typically need to do in post to give it the best look? As I played around, I used the following:
    -Auto Levels – I used auto cuz apparently I don’t know what I’m doing with regular levels (thought I did until I got better results with auto)
    -Hue/Saturation: upped master saturation by +21
    -Curves – added a slight S curve

    The problem is, areas of the image, it gave like a yellowish noise. So I had to use Denoiser II. Have you found yourself with similar problems? I’ve uploaded some samples at http://www.betterwaysoflearning.com/misc

    As you can see, in image 2 you can see a lot of yellow noise around the bowl. I think it was introduced when I upped the saturation.

    1. You really need to use a LUT as one of the key things that needs to be done is to move the color space from the very large S-Gamut color space to the much smaller 709 color space. If you don’t use a LUT you will get color shifts when you make saturation changes as the mapping of your colors will be incorrect. In addition adding an S-Curve is a type of gain adjustment and this can increase noise. A lut does not add gain, simply shifts levels so less noise is added.

  30. Sorry for asking, does I understand this correct, that in the camera for all the 20 LUTs is the same PP7 with the original manufacturers settings in it? So: PP7 with S-Log2 an S-Gamut? Or PP7 S-Log2 with ITU709-Matrix?
    thank you

    1. Those clips were shot with a pre-production camera where the native ISO was 1600, not the 3200 of the production cameras.

  31. Hi Alister thanks for this article it’s amazing… I have one query… I am shooting a narrative piece with lighting, however I don’t have access to any NDs for my cine lenses so I think 3200 on slog2 may be a bit high for my exposure. As such I was thinking about shooting on cine4… So would I set my exposure to 18% grey to the same as you would for slog 2? I’m kinda new to the Sony and log world so your info is a great help, any info would be great.. I’m also recording the 4K to the shogun if Hunan makes a difference so I have the waveform (which I assume has the %age levels on it – I need to check)… Thanks in advance, Nick

  32. Thanks for the detailed article on using S-Log2 gamma on the Sony A7s. The discussions of the technical limitations of Rec-709 dynamic range and H.264 bit-depth are concise and accurate and clearly illustrate the challenges involved in capturing high-contrast images on modern video cameras. I don’t doubt that the recommended techniques produce excellent results using S-Log2 gamma on the Sony A7s.

    One thing I found disconcerting was the example showing the results of over-exposure of up to 3 stops with S-Log2 gamma. I would expect this to proportionately boost shadow details with each stop of increased exposure. In your 4-pane comparison image, however, I see no perceptible improvement in shadow details, regardless of the exposure. Does the S-Log2 gamma and/or internal pedestal of the A7s truncate shadow details before exposure settings take effect?

    A second question I have is about the implications of the “native” ISO of the A7s being 3200. Does this mean that when lowering the ISO below that point, the camera uses digital scaling? If so, that would imply that unlike most other DSLR’s, lowering A7s ISO below 3200 does not increase its dynamic range.

    1. There is little difference to the shadows as you see them as the LUTs are always trying to return the image to the same levels, so the final pictures look more or less the same. But the LUT is just a starting point for the grade, you would be able to pull more shadow information from the brighter exposed shots by adjusting the images with additional grading.

    2. The sensor always acts as a limiter for the extremes of any cameras dynamic range. The upper limit being the point where the pixels overload or clip, the lower end being where the sensor noise becomes greater than the captured picture information.

      At the native ISO you will normally be taking black as the sensor noise floor and white as the clipping point. Lower the ISO and you are decreasing gain so any shadow information is reduced and you start to loose DR in the shadows. Meanwhile the sensor clip point remains the same, so DR reduces overall, the reduction in DR taking place in the shadows.

  33. having just made the transistor from f800 land to the FS7′, I’m wondering if your test assessment is applicable to the FS7?

    1. The FS7 is 10 bit so doesn’t have the same issues as the 8 bit structure of the A7s. However using a Low EI on the FS7 will help reduce noise after grading.

  34. You didn’t realize that the A7s is using analog gain. Hence, you are amplifying the signal before the 14bit-a/d-conversion (respectively 12bit with the electronic shutter) and therefore do indeed get additional shadow information out of the sensor by increasing the ISO number.
    Example: if you increase the ISO from 100 to 102400 on the A7s (ISO 100 would be ISO 640 with slog2, but not allowed), you still get reasonable images. This is an increase of 15 stops (+90dB). If you would do that digitally, you would have to sacrifice 15 bits for that. But you started with only 14, so you wouldn’t get any image at all.
    Conclusion: In a low light scenario (where all other methods of getting more light are already maxed out) it is mandatory to increase the gain to correct the exposure, not only because you are then leaving the compressed shadow-part of slog2, but because you are actually feeding the the a/d-converters with more real shadow information.

    1. May be a tiny bit, but it is the sensor noise that is the limiting factor and adding gain even before the A to D increases both noise and real picture information by the same amount, so there is no change to the signal to noise ratio, so the darkest thing you can see will still be determined by the sensor noise floor.

  35. I’m sorry, I did a mistake. ISO 100 to 102400 are +10 stops (+60dB). 14it-10bit = 4bit. But the picture has clearly more information than 4bit.
    Or try to boost an ISO 100 raw photo by 10 stops in post. The result will be much worse than shooting with ISO 102400 in the first place. I hope you get the point.

    1. The difference is easy to explain. 100 ISO Raw is 5 stops below the sensors native ISO so the shadows will be lost as negative gain is being applied somewhere in the cameras processing chain.

  36. How much is the signal to noise changed for the worse with s-log. Compressing the signal so that the full range from baseline to 100% is not used must increase the noise
    when the curve is reversed in post. What exactly is the noise penalty for s-log?

  37. How does S-log compare exposure range wise with a “normal” gamma when knee and knee saturation are properly used for the highlights and various black gamma settings for low lights?

    1. Generally the most you can squeeze into a standard gamma with knee is about 11 stops. If you keep the knee above skin tones and set it to 80-85% then to get close to S-log2 you would need to squeeze 9 stops into just 15 to 20% of your recording range which is going to look pretty grim. Even if you could bring the knee point down low enough to give a gentle enough slope to get a 14 stop range with a sensible amount of data you would still have the big issue of an image divided into two distinct ranges. The bottom half following standard gamma and the top half highly compressed. This then creates grading issues as the upper and lower ranges need to be graded independently for good results.

  38. It’s a great article, Alister! Don’t know why people insist on challenging your points and muddying the water. I have shot a considerable amount with the F3 in Slog2 and my tests showed pretty much the same result. I routinely rated the F3 at ISO 1000 instead of the native 1200 in Slog2. I found, as you did, exposing at ISO 1200 was generally too heavy a lift in grading unnecessarily unless I had a lot of highlights to worry about. I got less noise rating at 1000 ISO. I use a light meter to determine exposure. However, I found I could also judge exposure with zebras in Rec709 mode then switch to Slog2 and then leave exposure alone. It’s almost like exposing for film stocks. We would routinely overexposed a stop or two to reduce grain, but much over that was little or no benefit. Use to be we always had to slightly under expose digital to protect highlights but now we have log to do that. Thanks, again! Good work explaining it.

  39. Great, informative article. Not just for the A7S, but for learning about exposure and in general. This has helped me a lot. I feel like I have questions, but I’ll just wait for Part 2.

    Thanks so much!

  40. Thank you , i`m looking into switching from Canon 5D mk3 to A7s and i`m kinda afraid of S-LOG since i`m not really a colorist to know how to use this mode.

    1. Well you don’t have to use S-log2. The camera is still extremely good using the other built in picture profiles and in particular with the Cinegammas. S-log2 is just the icing on the cake for more advanced users.

  41. 1/6400 shutter speeds ? Obviously you can’t really use that with video footage.

    I understand everything here — except I’d like to see the same results with ND filters since using that kind of shutter speeds for 24fps is not appropriate.

    1. It would look exactly the same with ND filters. It would make no difference as there is no motion in the examples. I agree that you wouldn’t normally choose a shutter speed of 1/6400 for video, but for these static examples it makes no difference whatsoever.

  42. Really interesting but I really don’t think your final product looks very good. Proof is always in the pudding. It may be that everything is exposed correctly but it sure isn’t looking good on my screen. Maybe your points would come across better if the final outcome looked better. I have viewed a ton of tutorials and articles on the A7s and have to say the best looking footage I have seen, the guy took with PP7 with no modifications and used FCPX out of the box color grading. Being technical is one thing but people have to use their eyes to achieve the best results for them. Too many people I find are trying to get the cinematic look without firstly getting the video footage to look good first then go for the “Look”

    My 2 cents

    1. Obviously you are missing the point of S-Log2. It isn’t meant to look good straight out of the camera and it never will do.

  43. I was looking for more info about my new A7s and so I came across this website. Learned a lot by reading this article but since I’m a still shouter the whole thing was new for me.
    Will definitely use s-log-2 when possible. But actually I bought this because I’m leaving on a tour to Island and hope to photograph and film the Aurora with my new a7s.
    Will be possible to make great stills and time-lapses as well.
    Was already able to photograph aurora before,see https://lightroom.adobe.com/shares/3b39dd5e7f5f4328a6388d9837ba5cbf/albums/179c7dc71ceed7aec1df90cc9fa5bf92

    Settings here were for the most around 2000 ISO 6 to 10 seconds on a Canon 6D.
    So here comes my question: what would be the best settings for filming the aurora with the a7s.

    And hope there will be Aurora and of course good weather conditions ( it’s a lot I know)
    PS : I’ve no possibility for 4K at this moment ( will just use the camera)
    Great article and hope you enjoyed the coffee…

    1. Really depends on how bright the Aurora is at the time. It could be anything from 1/25th to 5 seconds and an ISO range from 400 to 6400 depending on what you are trying to achieve. There is no one size fits all setting.

  44. Excellent article and a lot of very useful information. Thanks for sharing your experience.
    I’m from Belgium and here it’s rather difficult to find any information about how to use the A7s for video in low light situations.
    But since I will visit Iceland I’m hoping to use this wonderful toy, the A7s, to catch the northern lights in movie mode.
    Could you please help me to let me know what would be the best settings. From what I understand the S-log2 doesn’t make any sense.
    Thanks to let me know

  45. In Slog2 the M.M indicator only goes up to +2.0, is there a way to make this go beyond this so you can easily expose +3? If you can’t do that, is there an easier way to measure 3 stops over?

  46. Hi Alister!
    As a new videographer, I read almost all your articles and enjoy them!
    You help me a lot!
    I set my FS700R ISO to 3200 with S-log-2 and record via Odyssey7Q+.
    My question: How many stops I loose when I derive the 4K RAW to 4K Prores 10-bit 4:2:2 directly via the settings of the Odyssey? Or is it the same dynamic range of both RAW and Prores (compressed) derived from directly from the Odyssey?
    It will be my honor to invite you for a coffee 🙂

  47. Hi, first of all thank you for this article. It’s well explained!

    I have one question. I went to a mountain with some friends at night, and I filmed them whilst they were taking pictures of the sky. There was very little light (camera monitors and some lanterns), and I tried to shot it with PP7 without knowing I had to pull up 2 stops to get less noise. So when I watched the videos, all of them look very noisy, as almost everything is black (mountains, sky, etc).

    So, should I have tried to go 2 stops above? If I had, I wouldn’t have noise anymore? Also, I have been able to do it yet, but when I push down the blacks in the computer, will I be able to reduce considerably the noise?

    I was shooting around 25.000 ISO, f.2.2 and 1/50.

    Thank you very much!

  48. dear Alister,
    many thanks for the awesome info.

    new to the a7s and trying to get the most out of the tech- do you have a suggested ‘go-to’ picture profile setting for bright light environments and low light environments (shooting video)? i have had some success (for bright light environments) working around ND filters -using all the same s-log2 settings but changing the colour space to cine 2 or 4, leaving the gamma as s-gamut, enabling me to shoot below ISO 3200.

    thank you again for your generosity. i admire your knowledge, and aspire to wrap my brain around some good portion of what you know.

    1. I use the cinegammas for most things as they provide better highlight roll off. If using S-log2 at an ISO other than 3200 reduces the dynamic range and defeats much of the point of using S-Log.

  49. Hi Alister,

    Thanks very much for a great site full of information. I promise to buy you a six pick if you would be so kind as to impart some of your hard gained knowledge on Slog and the FS7. I am shooting part of a story next week and am working on Slog/Cine EI for the first time.
    When switching on to Slog/Cine and exposing the picture correctly in the view finder and then watching the pictures back, they look overexposed … is this normal? Also I can only adjust white balance in the A/B/Preset positions (3200/4500/5500 respectively) will their setting affect the colour grading process in post?
    Thanks and cheers

    Leander SD

  50. Hi Alister,

    Thanks very much for a great site full of information. I promise to buy you a six pick if you would be so kind as to impart some of your hard gained knowledge on Slog and the FS7. I am shooting part of a story next week and am working on Slog3/Cine EI for the first time.
    When switching on to Slog/Cine and exposing the picture correctly in the view finder and then watching the pictures back, they look overexposed … is this normal? Also I can only adjust white balance in the A/B/Preset positions (3200/4500/5500 respectively) will their setting affect the colour grading process in post?
    Thanks and cheers

    Leander SD

    1. How are you setting the exposure? Are you using the 709(800) LUT and EI at 2000? Anything else and the exposure may be off. But this might be deliberate as over exposing S-log a bit is normally a good thing.

  51. I do understand – I was referring to – in each trio of shots you show the corrected via 709 LUT – those are the images I was referring to. Are those not there to show it after it is off the camera?

    1. No color correction or anything else was done, just a by the book S-Log2 to 709 conversion. 709 is 709. The LUT moves you from log space to 709 space, bringing the color space down from SGamut to 709 and scaling the mid tones correctly so that the display contrast is true to life. Once in 709 space, assuming your going to be viewing on a 709 display then you can do your creative grade from their. No color correction or anything else once done, just a by the book S-Log2 to 709 conversion. If you don’t like the look then you can use a different LUT, that’s the beauty of Log.

  52. Hi Alister,
    After your permission, I will repeat my question cause I did not receive an answer yet:
    When I set my FS700R’s ISO to 3200 with S-log-2 and record via Odyssey7Q+, how many stops I lose when I derive the 4K Prores 10-bit 4:2:2 directly from 4k RAW via the settings of the Odyssey? Or is it the same dynamic range (14 stops DR) of both RAW and Prores (compressed) derived directly from the Odyssey?

  53. The base ISO for raw of the FS700 is 2000 ISO. If you double the ISO you will loose 1 stop off the highlights, if you halve the ISO you will loose 1 stop from the shadows.

    So at 3200 ISO you will have around 13.4 stops of dynamic range coming out of the camera. Then if recording ProRes on the 7Q it depends on which gamma curve you are using. If using S-Log2 then you will also have 13.4 stops. If you are using 709 then much less.

  54. So I have to set the FS700R ISO on 2000 instead of 3200 in order to get 14 stops DR (unlike the A7S).
    Thank you Alister for this important information, and most important that the prores and raw’s DR are the same when they are set via the the 7Q.

  55. Hello Alister,

    I find this article of utmost help to budding filmmakers like myself. Please explain to me further about setting the +2 over exposure.

    1. When exposing +2, can I just look at the MM, and when it hits +2 does it mean Im already +2 over exposed (in Slog2)?

    2. Why do I need to do some calculations? if the MM already says if Im +1, or +2 over exposed?

    Many thanks for this helpful article. Would be nice to get a reply.

    Kind regards,

    1. If MM says +2 then you are two stops over exposed. Ideally you want to be around +1.5 to +2, not more than +2.

  56. dear Alister,
    thank you for taking the time to respond:) do you have an ND filter recommendation for the bright light work? i saved up and just purchased the SONY 28-135mm lens… hoping to get the most out of this big guy.

  57. Blazar’s comments reflect my experience, I can’t see that he is “missing the point”, he is trying to put forward a balanced view by a knowledgeable professional.

  58. I’ve been looking for information on Sony A7s S-log2 and exposure for quite some time. I’m glad you published this… very helpful.

    Too bad some prefer to quibble about other methodologies instead of adding value to your approach.

    Keep up the sharing… iced coffee is on me.

  59. Alister,
    Thanks for the information.
    I have a modified a7s with an active cooling peltier chip/heatsink/fan and can tell the noise is drastically reduced compared to one that is not modified.
    1. Does this give me more latitude to increase the iso and still benefit from the dynamic range of Slog2 (due to the different noise floor)?
    2. If I am shooting videos of the night sky (dark sky to faint stars to bright stars) does this qualify as a needing the extended dynamic range of slog, or is it better to up the iso to seemingly capture fainter stars and therefore I should use a different colorspace/gamma? My bright lenses are already wide open.

    1. Increasing the ISO limits the DR in the highlight range. A lower noise floor may help compensate for this a little, but I still THINK you will loose DR when you raise the ISO. But shooting the night sky I doubt very much that you need more than 5 or 6 stops of DR unless the moon is in the shot. As a result I would not use S-log and would use standard gamma (more bits per stop) and raise the ISO until noise becomes objectionable.

  60. Hey Alister,

    thanks for the guide, and enjoy the Latte!

    I´m kinda used to shooting with the FS7 in Cine EI mode setting the exposure with Zebras set to 61% metering a white card.
    I got a question concerning metering the exposure with Zebras with the A7s since my next project is on a smaller budget and we´re shooting with the A7s.

    I haven´t shot with this camera so far and I don´t have it in front of me right now, so it´s totally theoretically.

    You specified that the IRE for the white card at S-Log 2 +2 is 83%. So couldn´t I just set the Zebras to 83% and adjust my ND / Iris as long as the Zebras start to show on the white card?
    I´ve been working this way on the FS7 for a while now and it worked great for me so I wonder if it works the same on the A7s?

    Cheers from Germany

    1. Yes, that would be another way to work. Just remember that zebras have a 10% wide window, so you could be over a stop out, although provided that doesn’t put you 3 stops over you should be fine. I might play it safe and set zebras to 78%.

  61. Hey Alister,

    I bought a 478D light meter recently. So I decided to give the 478D DTS software a go. This software can calibrate the light meter pair with the camera by using colorcheker passport .After I did every thing the software said. I find out they only show 9.3 total Dynamic range in the software by using slog2. Interestingly , after I upload the profile to the light meter. I use the meter to measure the exposure for mid grey lets say it’s read at F5.6 After I dial the number in to a7s and then use the in camera spot meter to read the exposure to the grey card it says overexposed by 1.7 Stops . Like you discovered when we shoot in slog2 weneed to overexpose by 1-3 stops in oder to get a clear image.So that’s mean the meter reads the correct exposer for a7s slog2 after calibration? Which also meaning the in camera meter is not that accurate?

    thanks for all your work

    1. The cameras meter is normally very accurate and this can be checked with a grey card. It’s impossible to measure dynamic range accurately with a colorcheker. You need much more sophisticated back illuminated charts shot in total darkness. It does not surprise me that the software you have is saying 9.3 stops and I really wouldn’t be concerned about that.

      The thing that matters is: If you use you light meter, are the results satisfactory? If you are getting good results I really wouldn’t worry about any disparity between the camera and the meter.

  62. Hi Alister,

    Thanks a lot for such detailed article… read a year worth of info and comments within a few hours really take a lot of brain juice to break em all down.

    I am sure someone have asked you this question before but with the new A7r2 shooting with Slog2 and S-gamut, does the same theory from your a7s article apply to shooting with A7r2 at all?
    With the native ISO being 800, I do notice that shooting with s35 mode the noise in higher ISO settings seemed much finer than FF and is useable upto 10000 ISO (IMO). Any suggestions on which ISO setting I should be working with to get the most DR from s35 mode?

    Thanks in advance and a coffee to you sir.



    1. The same theory applies to both cameras. For maximum DR you always want the native ISO, but if you find you do get a more pleasing result at a lower ISO there is no harm in doing that, you will be loosing a bit of DR in the shadows, but if the noise is effecting your shadows anyway, then it’s really not going to hurt using a lower ISO.

  63. Hi,
    Very nice and useful article. I learned a lot with it but Ihave some questions :):

    I just get the A7RII. Watching other videos with it I found some very nice results at different iso (other than 3200). For example this one at ISO 800:

    One more question, maybe it’s new for the A7RII but when I activate PP7, XAVC 4K but my output file is .MP4. Is this normal?

    Also would you prefer working with SRVB or Adobe RVB? What is better? Adobe RVB?

    I tried your Luts in After Effects and they worked very well.


  64. Alister,

    I sincerely appreciate your work here trying to illuminate what is a very confusing subject. LOG is coming to my GH4 as well so there’s a lot of discussion about it in our group, with about 1000 theories on what it is, how it works, and more.

    I read this article with a voracious appetite because it’s clear you understand this very well, and I also appreciate your responses to all the comments- showing a genuine desire to help people learn.

    The top chart shows how the limited range of Rec709 chops off additional bright values and dark values. I’m confused by the first chart that talks about compressing the greater dynamic range (above the part starting with S-Log) into the limited Rec709 space. (Image numbers would help when referring to specific images and charts)

    In the initial image with you, we can see that the white clouds are clipped.
    But also note that they are white-
    or at least at the top part of the Rec709 values.
    Then in the S-log images of you, the clouds are not clipped
    But also note that they are far from white
    Nowhere near the top of the Rec709 values.

    This does not match the chart where you say those additional two stops of bright latitude will then be squeezed into the Rec709 space (since that’s what the 8-bit camera H.264 codec records). So, since we now see un-clipped clouds, shouldn’t they now be at the top of the Rec709 whites? Those extra two stops smooshed down just under the limit?

    But in “getting your exposure right”
    you note that 90% white would be at 59% in S-Log,
    Middle Grey down to 32%
    The histogram shows almost the entire top half not being used.
    I assume that the histogram is calibrated solely to Rec709 space so everything in log appears vastly underexposed. But if the histogram shows 90% white down at 59%, then how does that corroborate with your charts showing how whites formerly clipped would now just fit into the top of the Rec709 space?

    I mean, even with log, dynamic range is not infinite.
    Bright values still have to clip somewhere.
    Especially if (as discussed later) we push the exposure.
    But when the image clips in any log footage I’ve seen, the clipped video is still nowhere near the white point of Rec709- despite your charts saying that these values are being squeezed in at the top of the Rec709 range.

    So I’m looking for clarification as to what appears to me to be disparity between your charts showing how the greater dynamic range is recorded in 8-bit space, and much of the information in the rest of the article showing that log uses only around 50% of the available 256 steps.

    If the charts indicated that log footage existed in a range _in_the_middle_ of the Rec709 space— not extending anywhere near full white, or full black. This would corroborate with using a lut on a monitor to try and see what the LOG footage would look like when _stretched_back_out_ to Rec709.

    If log in 8-bit, long GoP recording fails to make efficient use of the limited space has, this gives even greater importance to what you say about how under and over exposures can quickly mess skin tones up. If log indeed use all 256 steps and “filled up” the Rec709 space, then we’d have considerably more data to leverage when grading.

    I look forward to your clarification on this.

    1. In short what log does is take the normal 0-100%, 6 stop range of Rec-709 and squeezes that down to fit in approx 0-65%. That then leaves 65% to 109% for the extra dynamic range that log can capture. S-Log2 clips at 109%, S-Log3 clips at 94%.

      Histograms are not calibrated to any particular gamma, they simply measure actual levels recorded between 0 and 109% a historgram will not show dynamic range only the recording level.

      The clouds in the S-log picture are not clipped because the gamma curve has enough range to capture them without clipping. The shot is exposed at the nominal correct exposure which puts white at 59%. Then the clouds are above that, but still well within the range of the gamma curve so they never reach clipping. Then when you apply a standard 709 LUT the white at 59% would be converted to 90% and the clouds which are much brighter would now clip once more. The data would be there in the file, but we don’t have the display technology to show the full captured range. This is where the expertise of a good colorist come in as he/she can then manipulate the extended range data to make the clouds and sky look good. But however it’s done the contrast in the final image in the sky will not be natural due to a lack of display contrast.

      This is why I am very excited about new HDR display technology that’s just starting to hit the market as these new displays will actually be able to show a lot more of the range that these cameras can capture.

  65. dear alister. thanks for all this know how :). i`m a beginner in this s-log2 thingy, and so i`m reading every article and watching every video i can find about this.

    i have an RX100IV, which is a great pocket film camera for me. you seem to be a sony pro. what do you think : is your article 1:1 usable for my cam?



  66. Incredibly helpful. Shooting a short on the a7S this week. I used this tutorial to get dialed in with the camera on a test shoot last month. You’ve given me a great amount of confidence going into this shoot. Thank you so much!

  67. Thanks, man! I just learned a TON.

    I’ve got 20 years of professional audio engineering and music production experience and never owned a proper camera until this week, so all of this patiently well-stated, precise info is exactly what my engineer brain needs. …Time to go practice now!

  68. Hi Alister

    Brilliant work has really helped me and my video work is looking much better and less noisy but I have one question, I am using an A7ii and wanting to know
    if the native ISO is 3200 like the A7s or if this is different as it is a newer model.
    I can’t seem to fine out if this is the same anyway online as people are quoting the native ISO as the total range from the lowest setting to the highest.

    If you could help me with this it would really help me and be much appreciated.

    Cant wait for part 2
    Many Thanks

  69. Pingback: WR-121-38
  70. Great article. Is Part 2 available yet? I get the camera (input) log gamna and gamut profiles, and get the input LUT mechanism for the clips into the non-linear editor, but just need to understand the output gamma and colour gamut to be chosen (transformed to). For instance, do we use a LUT target to 709 or sRGB when bringing the clips into Sony Vegas (for instance), which uses an internal sRGB colour model I believe. And we actually use Full Levels (cRGB) as all of our rendered video goes to computer screens on the internet (not TV). Is Part 2 out? Just need to understand which output gamma and gamut to chose in 3DLUT transform. Please advise.

  71. Have been reading about slog on the web, but your article, Alister is really excellent!
    Sony recently released A6300 and the reviewers are crazy about it, similarly to the other recent Sony cameras it has slog-2 and 3.
    The videos and articles so far, about applying slog to a6300, lack the depth of expertise I see in your post about the Sony professional cameras. Do you think your pack of LUTs can be used directly for a6300 or the LUTs will have to be reworked?

  72. Fantastic article! Well structure, clear explanations!
    I work in post for feature films for about 4 years, and in this new era of digital world, we need specialists as you to clarify so may confused infos!!
    And what you state is soooo true!
    Is part 2 available yet? how can I get it

    Thanks so much

  73. Interesting reading. A great illustration of how many folk are successfully “using” these features, often without really understanding fully just what is happening – myself included!
    BTW, the verb in this context is “affect” not “effect”. (Sorry, just a pet hate of mine!)

  74. Thanks for your article. It means a great deal to the community of a7s users.
    I have a question if you don’t mind. If i want to shoot slog2 in low light should i stick to the 3200 ISO?
    Your previous comment advised against it. If i can’t shoot low light with the slog2 profile, who is suitable?

    Thanks for your profound insight

    1. S-log is a poor choice for low light. As soon as you use a ISO different to the native ISO you are no longer getting the cameras full dynamic range, so using S-log becomes pointless.

  75. Thank you for this very helpful post Alister. The table captioned “My suggested exposure levels for the Sony A7s. The “sweet spot” is from normal to +2 over” is marvellous. Do you have a version for S-LOG3? I’ve never seen IRE values for middle grey > average skin tone > 90% white laid out so clearly both in comparison to Rec-709 and with the percentage increments for pushing/over exposure.

    Many thanks for all your hard work, illuminations and clarifications.


  76. As a newbie in video here, I have a basic question on “native” ISO. This article talks about the A7S’s native ISO of 3200. What about the A7R II? What is that camera’s native ISO? And, in general, how does one find out what a camera’s native ISO is?

  77. Thanks for such detailed explanation. Almost all the doubts are clear, however its become a need to use ND filter for slog 2 especially in outdoor and even surprised to use sometimes indoor as well, I know its because of the ISO 3200 is the lowest you can go. In the end Thanks again.

  78. This is a very informative article. But I remain confused about all this.
    If I am shooting in S-LOG and I want to overexpose by two stops over the “correct” exposure, what am I adjusting exactly when I turn the Exposure Compensation dial? It is not the ISO, shutter speed, or aperture, is it?

    Do you really see that much of a loss in dynamic range or qualitative difference between shooting video in PP5 or PP6 versus PP7?

    Does PP5 or PP6 break down under grading?

    What really confuses me is why, under PP7, the ISO locks down at a minimum 3200, and under all the settings, it remains adjustable. Why is it necessary for the ISO to come up so high?

    Thank you very much for your work.

    1. ISO gets locked because you will only get full dynamic range at the sensors native sensitivity. There is a clear difference in DR between the different gamma curves. How the compensation applied by turning the compensation dial will depend on what mode the camera is in. In aperture priority it will be the shutter etc.

  79. Really great tutorial. So, if I wanted to get a “proper” exposure not in S-Log, but in, let’s say, Cine 1, I could still use the method you describe above? Set the Metering Mode on spot, use an 18% gray card, and then make sure the Exposure Meter (MM) is showing at 0? When the Picture Profile is set to Cine 1-4, is the Exposure Meter setting zero at the appropriate level of Middle Gray? Or would I need to eyeball the histogram to get a sense of where I might be in terms of middle gray? From what I’m reading in the manual, it sounds like the Cine gamma modes also require proper exposure around middle gray, like Cine 1 around 30% or so. Would you also recommend pushing the exposure on the Cine gammas too? Thank you very much.

    1. The camera always knows what the appropriate base middle grey level is for each curve, so MM 0 for a grey card will always be the nominal correct exposure. I would not push the cinegammas brighter as they have a knee/roll-off that reduces contrast and if you expose brightly skin tones start to go flat.

  80. Alister amazing mate the best , understandable article on this subject on the internet. I am a wedding film maker using A7s, A7rii and soon 6500. I use the A7s on the gimbal because lack of stabilisation. It tends to be the case that we have to use some of the automatic functions of the camera because we are moving around so much on the gimbal. Obviously the light changes on the move and it’s impossible to keep changing the camera settings. How would you play it in this situation considering the fast pace of the wedding day that could be 10 hours plus long. From what you have said would you advise me to lock the ISO at 3200 shutter speed at double the frame rate and let the camera use the aperture within a range to manage exposure at +2? I would also use Snap on and off ND filters outside in very bright conditions. Would you then say as the light goes and we move inside I should switch to Cinemagram 4 and where possible add light ? On all of the other cameras on monopods or tripods I can just use full manual . I am also looking at the A7s Ii and what do you say Slig 2 or 3 is better for weddings? Thank you so much for using your time to write such informative articles. It’s part two finished or are you still working on it. Cheers

    1. If shooting with log you must lock the ISO to 3200 on the A7s. Shutter speed can normally be anywhere in the 1/50th to 1/100th range for a wedding or similar event where there isn’t a lot of fast movement to show up the difference between 1/50th and 1/100th. Then use the aperture to control exposure combined with ND filters. Don’t allow the aperture to go smaller than f11 as you will get soft pictures due to diffraction. S-log2 works better with the internal recordings as you only have an absolute maximum of 235 shades. S-Log 2 uses approx 225 shades while S-log3 only uses around 200, which is not a lot of steps for 14 stops.

  81. Hello Alister,

    I would like to consult with you about some question.

    That’s say we all know that when shooting a7s ii we better use slog 2 instead of slog3 because the 8 bit. However how about shooting format. If I want to deliver 2k only should I just shoot in 2k 60M or shooting 4K 100M and downscale in post? There are a lots of people out there say it’s better to shoot 4k and downscale in post. However I doubt with that.

    Background: A7s ii with Atomos Assassin HDMI output ProRess 422, slog2

    1. The A7S does a pretty good job of downscaling to HD internally and the 60Mb/s codec is pretty good. However shooting in 4K allows you to use a very high quality downscale process in post that can exceeded the quality of the internal downscale. Compression artefacts exist in both the HD 60Mb/s footage and the 100 Mb/s 4K. Downscale the 4K and the compression artefacts are made smaller and become less visible. Also both codecs are 4:2:0 so it is better to start with 4K 4:2:0 and downscale.

  82. Hi Alister! Thanks a lot for all your clear and helpful content. I’m just starting understanding this whole new world.

    Still I’ve got few questions:
    1) I don’t understand why you loose dynamic range by increasing native ISO (btw on my 6500, base ISO is 800 for both S-LOG2 and 3, isn’t it better?)
    2) Does this rule of never increasing native ISO apply for cinegammas (cine1, cine2, cine3, cine4, which are 200 ISO on my 6500)
    3) As increasing the dynamic range does decrease the quantity of information in each stop, would you recommend to record REC709 for a scene that has no more stops in dynamic range that REC709 is capable of handling (8 stops, is it?), or would you still prefer a cinegamma?

    Enjoy your premium beer 😉

    1. Thanks for the beer!

      The sensors output range is very carefully mapped to the cameras 0 to 100% recording range at the native ISO or 0dB gain. Any ISO change on an electronic camera is some form of gain change (the sensor itself cannot be changed to change the sensitivity so we must add gain instead). Increasing the gain or increasing the ISO amplifies the signal from the sensor by more than at the base sensitivity. So the brightest things the sensor can see will be amplified and as a result exceed 100% and therefore cannot be recorded anymore. Meanwhile at the bottom end of the range the limiting factor is always noise. Adding gain will make things brighter, but it will also amplify the noise, so in reality you won’t see anything extra. So at the top end raising the gain decreases the dynamic range as bright stuff will go beyond the peak recording limits but in the shadows you won’t see anything extra, so the dynamic range is decreased.

      2: Yes, increasing the gain will normally reduce the DR of all gamma curves.

      3: Generally it is better to use the gamma that best “fits” the dynamic range you are recording. However it’s never quite that simple as different gammas handle highlights in different ways with different approaches to highlight compression. Rec-709 with no knee is 6 stops and excellent if the scene only has 6 stops. But go beyond 6 stops and the knee kicks in which can lead to bad looking highlights. A cinegamma might give more pleasing highlights.

  83. Thanks a lot for this awesomely quick and detailed reply. Watched the vocas yesterday, it was fantastic! I’ll have to watch it again. This “never beyond base ISO” rule for gamma curves has been obsessing me for these three past days. I couldn’t solve this low light scenario where your shutter speed, aperture, and external light hit their limit. I think I came to understand something though. Correct me if I’m wrong : in a scene of 5 stops lacking in light, with a REC709 gamma that can take 6 stops, pushing the ISO may make me loose 1 stop of dynamic range but it won’t be a problem because this stop is not in my scene, and by doing that I will have a brighter footage, which will help me in post, because I won’t have to tweak the shadows too much. Same for a cinegamma in a scene of 9 or 10 stops (where cinegamma cat fit about 11). When you say to always use the native ISO for gamma curves, you only mean in the case you already have your histogram filled from black to white, is that correct? Shouldn’t hurt to tweak the ISO if there’s some room on the right of the histogram…

    Or is it still better to keep the native ISO, hence having a darker footage, and to turn the whole exposure up in post. Which method will give the best result?

    Sorry for drifting from the SLOG topic by the way, but from my understanding, my 8 bits camera doesn’t allow me to play with these curves much…

  84. Hi Alister,
    what are the best practices for recovering cinegammas highlights in the 100-109% range in Premiere Pro/Lumetri?
    If i take that 109% clipped whites down to 100, and than i fiddle around with the other sliders (or curve) to get the same brighness levels ’till 80-90% i get an abrupt rolloff to clipped whites instead of the nice soft rolloff i’m looking for…
    I’d love to know what’s your workflow…

    1. There isn’t really anything that you can recover from that far up. The curve is cramming a couple of stops into a tiny data range to provide what would normally be a pleasing roll off. The down side to that means there is a huge amount of scene range is recorded with at tiny amount of data so if you try to exapnd it to restore the correct contrast it becomes coarse, steppy and often either On or OFF with no texture. This is why Log behaves totally differently as log does not have a roll off, so even the very brightest stop contains plenty of picture information.
      The key to working with Cinegammas is correct exposure, which means a white card exposed down at 70% and skin tones around 55-60%. That way your whites and are below the roll off and it’s only extreme highlights that will be in the top of the curve.

  85. just read this on sony’s webiste: “For example, you can shoot at 1 EV brighter than the standard S-Log2 exposure and then darken the footage at the same value during grading. However, it should be noted that the dynamic range will be narrowed by half in such situations”

    So do we actualy lose dynamic range when overexpose?

    1. That statement from the Sony website is incorrect. You don’t loose any dynamic range when you shoot a bit brighter, after all you are not changing any of the camera settings and it is the camera settings that will change the DR, not how you expose. But by exposing brighter you will reduce the highlight headroom – at the same time gaining what you loose from the headroom in an extended shadow range.

  86. Hello, thank you for your in depth article.
    I must say I come from Photo world and Canon to video world and Sony. Im still quite far away, but I touched some basics with Slogs and LUTS.
    I must admit I dont understan how to properly expose with Sony a7 camera, if I dont have device for HDMI that you mention.

    If I buy 18% graycard, how to find right exposure? 32% doest mean anything for me, how can I set that 32% in camera?


    1. In any auto exposure mode the camera will try to expose at the correct level for the gamma curve chosen. To measure the exposure of a grey card accurately you would need to get an external monitor with a waveform display.

  87. Hi Alistair,

    Thank you for all this. Helped me a lot back in the day.
    One thing though. Are you sure about the 6 stops of latitude above middle grey.
    I did latitude tests myself (on A7s & a6500) and in most situations the clipping into 109IRE starts at +5.3 stops.
    Thanks and kind greetings!

  88. Great article, thanks.

    Regarding your statement “In addition you should ALWAYS use the cameras native ISO which is 3200 ISO and it is normally preferable to use a preset white balance.”

    The A7s’s native ISO is actually 100, with a second-stage dual-gain ISO of 2000. The way Sony implements S-Log is to read the sensor out at near base ISO but report the higher nominal ISO based on the shifted middle-gray region. For example on the A7sII the S-Log3 nominal ISO is 1600 but the camera actually uses an analog sensor gain ISO of 200.

    You can see this by examining raw files taken with the camera – fortunately Sony supports the S-Log picture profiles for raw stills. If you take two raw images with the same physical exposure (aperture/shutter speed) and at the same ISO 1600, one with S-Log3 and another without a profile, then examine the raw data in a utility like RawDigger you’ll see the S-Log3 image raw levels (ADUs) are approximately 2.5EV to 3.0EV lower than the non S-Log3 image.

    Additionally, if you examine the EXIF data using a tool like exiftool you will discover two separate ISO fields – a nominal ISO and the actual sensor-gain ISO. When no picture profile is used the two are always the same but with S-Log3 the nominal ISO is 1600 whereas the reported sensor-gain ISO is 200.

    It’s the lower lower sensor-gain ISO for S-Log that allows the extra highlight headroom, and it’s the S-Log tonal curve applied to the resulting demosaiced and processed data which allows that headroom (plus shadow room) to be squeezed into the 8-bit encoded video data.

    1. None of the above is relevant when shooting log video, and it is not gain that affects dynamic range but exposure.

      Gamma is a gain curve and the gamma (gain curve) is applied to the sensor output and it is the combined gamma gain + sensor gain that is important to the end user shooting video as they are unable to use raw. You wouldn’t set an A7S to 100 ISO when shooting S-Log video as you would have no headroom.

      Gain does not determine the dynamic range of a sensor. The size of the image well along with the size and efficiency of photo diode, along with noise determines dynamic range. This along with the integration period determine exposure. Gain is added after this and can make the signal bigger or smaller but cannot increase DR, only ever reduce it if you add too much. So the only way to extend the high light range is through putting less light on to the sensor so it saturates later, but this comes at the expense of a poorer SNR. The reality is that the A7S when set to S-Log2 is designed around a practical ISO rating of 3200 which you must remember on an electronic camera such as this is NOT a sensitivity rating, but an exposure rating. Compared to the standard gammas rated at 800 to 1600 ISO this means the operator will put less light onto the sensor and less light onto the sensor means the pixel will saturate later and the highlight range becomes extended as a result. This has very little to do with gain and everything to do with how much light you allow to fall on the pixel, which has a fixed conversion efficiency and fixed maximum signal limit.

      So the bottom line is – use the camera as designed. When shooting S-Log2 video set it to 3200 ISO so the full range of the signal from the sensor is correctly mapped to the full range of the video output and you will achieve the full dynamic range, plus the lower light levels at the sensor resulting from the higher ISO rating gives an increase in highlight range but at the expense of a worse SNR.

      1. Thanks for the detailed reply. We’re pretty close to full agreement. The main point of my post was that the native sensitivity of the A7s sensor is not ISO 3200 but ISO 100, for both video or stills – again, ISO 3200 is the nominally reported ISO for S-Log, which we both agree is used in that context as an exposure rating rather than relating to the gain of the sensor. For the purposes of your video-centric article it might indeed be more helpful to describe ISO 3200 as the “native ISO”, which in a sense it is for S-Log since it’s the native EXPOSURE ISO, but in terms of sensor property it is not, and the term “native” when discussed with ISO has connotations of sensor gain properties rather than exposure. The discussion is complicated by the double-duty of the term ISO – by definition it is ultimately an exposure measure, as you pointed out, but in practical terms ISO as set in the camera also directly ties to sensor gain. In non-LOG shooting the camera’s nominal ISO matches the sensor gain ISO, but does not in LOG shooting.

        The purpose of distinguishing nominal vs gain ISO in this discussion is how it relates to noise. There are two primary components to noise from image sensors – photon shot noise and electronic read noise. The former is determined only by the physical exposure (aperture and shutter speed) and is independent of ISO. The latter is determined by the sensor readout electronics and on the A7s is highly dependent on the sensor gain ISO.

        If we shoot the identical scene twice on the A7sII, once in PP0 (non-Log) and again in PP9 (S-Log3), using the same physical exposure and nominal ISO for both, and then normalize the video in post to match the IRE of the deep shadows (ie, counteract gamma curve differences), the PP0 recording will have noticeably less noise than the PP9 recording, particularly in the shadows. The amount of photon shot noise will be the same since that is a function of total light collected. However the electronic read noise will be much higher in the PP9 recording due to the specific sensor-gain properties of the A7s – as sensor gain ISO increases, the A7s’s input-referred read noise decreases, and since PP9 uses a sensor gain of ISO 200 for its nominal ISO of 1600 vs a sensor gain of ISO 1600 for the non-LOG recording, the PP9 recording will exhibit much higher read noise, which in terms of effect on visible noise will manifest as noticeably higher noise in the lower tones (shadows) of the footage.

        1. In the article I do indeed describe 3200 ISO as the native ISO for S-Log2.

          PP9? The A7s only has 7 picture profiles. Are you talking about the right camera?

          And if you shoot video of the same scene at PP0 and PP7 you will have completely different dynamic ranges. Sure you’ll have less noise with PP0 but you won’t have the ability to record the large dynamic range available at PP7 with S-Log2.

          Plus from a real world usage point of view, if you’re using the recommended camera settings you wouldn’t expose PP0 and PP7 the same. If you did, one of them would be incorrectly exposed and each profile is designed to serve a different purpose.

          I’m really not sure what the point of everything you have written is, other than an attempt to confuse people.

          The bottom line is, if you want to shoot video of a scene that has 14 stops of dynamic range you need to use the cameras S-Log2 native ISO rating of 3200. This does indeed result in a noisier image than the other more constrained gamma options, but you can offset this if you wish by exposing brighter then bringing the image down in post to improve the SNR. Depending on how you do this you can make your own decisions on how you split you shadow/highlight range and balance this against noise.

          1. I stated the A7s II is the camera being used in comments and examples, which has PP9. The same principles apply to both cameras for their respective supported log profiles.

            The point of everything I wrote is for shooters to understand how ISO is uniquely implemented for S-Log, and how that unique implementation creates additional noise independent of just the exposure differences. “Exposing the image brighter” doesn’t completely offset the additional sensor readout noise from how S-Log’s ISO is implemented, for reasons I described in detail in my previous post.

  89. There is nothing unique about how ISO in S-Log2 is implemented on the A7S. Every video every camera in existence carefully balances sensor sensitivity with gain to achieve a recording that fills the recording bucket with a signal of appropriate dynamic range. Change the dynamic range you wish to record and you have to alter the amount of gain you use if you want to keep that bucket full. This may demand operating the sensor differently for the optimum results. That’s nothing new and not special.

    What you have written, at great length, is from the users point of view irrelevant because the end user cannot change the way the sensor operates and if the user wants the maximum available dynamic range they have no option other than to shoot using S-Log with the camera set to the correct base ISO.

    Expose brighter and you will get a better SNR, that’s what the user needs to know and understand.

    1. There is precisely something unique about how ISO is implemented for S-Log – it uses a lower sensor gain ISO (200) for a nominal exposure level of ISO 3200. For non-log profiles the camera’s sensor gain ISO and exposure level ISO are the same.

      The relevance to users of this important distinction is for all the lighting situations that sit somewhat below the very high contrast scenes that require S-Log. Take for example a moderate-contrast low-light scene that requires an exposure level of ISO 1600 or 3200 for proper rendered brightness. A shooter unfamiliar with the read-noise penalty of using the lower sensor gain of S-Log’s ISO 3200 might decide to use S-Log at ISO 3200 rather than a non-log profile’s ISO 3200, thinking they were identical in practice, which will result in noticeably noisier footage even after adjusting the physical exposure of S-Log to match the non-logged profile. The difference again is due to A7s/A7sII’s noticeably lower input-referred read noise at higher sensor gain ISOs than at the sensor gain of ISO 200 used by S-Log.

      1. Whatever.

        Given that if they switch to another curve the gamma and thus gain will be different anyway, the user will see for themselves that the ISO performance will be different.

        Virtually every single camera that offers an extended dynamic range as well as a more conventional narrower range behaves exactly the same as the A7. F5, F55, FS5, FS7, C200, C300, C500, A6300, A6400……….. Nothing unique going on with the A7S.

        1. I agree, this behavior isn’t unique to the A7S/A7SII although the extent at which the noise performance differs between near-base and higher gain ISO varies across cameras depending on how ISO-invariant their sensor performance is.

          Although we may disagree on this partial matter I want to again commend you on a great article. I appreciate you providing a forum for my comments and taking the time to respond.

  90. Hello Alister,

    Is the native ISO when shooting SLOG 2 the same (3200) when using the A7III? It seems people are saying it’s native ISO is 800?

    Enjoy the coffee,


  91. Wow this is an amazing tutorial!

    I have found +3 stops over middle to be ok. Im using a A7s and A7sII. Does any one has a custom S-Log profile to use in and one to use outdoor for best results in post?

    Thank you once again for an excellent tutorial.

  92. I have the A7RIV.
    Base ISO on SLOG2 is now ISO 500 and on Cinegamma 1/2/3 it is ISO 100. ISO 200 in Cine4.

    Alistair, In your reference shots and suggested exposures you state:
    SLOG2 + 2 stops would meter at 55% middle grey and white at 83%. When I test my camera to spot meter at 55 on middle grey (+2 on camera meter) using camera zebras/ external waveform the white card on my calibration chart simultaneously reads at 76.

    How are you getting into mid 80s on white with 55 on grey?

    Many thanks

    1. S-Log2 is approx 12.3% per stop above middle grey. There are a little under 2.5 stops between middle grey and white. So when middle grey is 55%, white will be approx 83%. The cameras internal metering is not the most accurate. 76% is only about 1.7 stops above 55%.

      1. So for clarity on numbers… above middle grey to clipping 32 > 109 . 6 SLOG2 Stops. (12.8% per stop)

        32 % Native middle grey
        57.6 White ( or around 63% to be more accurate)

        Q1) At +2 exposure then we have 70% between grey and white for skintones – would that be placed on the brightest or darkest area of skin?

        Q2) As base ISO is 500 on the A7RIV, am I correct in saying that if my exposure ends up neeeding a push up and over ISO 2000 my dynamic range is reduced to 11 stops and hence no better than using Cine instead of SLOG2? Or would the highlights still be better in SLOG2 as no roll off ?

        Q3) What % is middle grey and white officially with Cine3 ? Can’t find any data on this gamma.

        Thanks so much for your help!

  93. wonderful article! not sure if I am the only one still shooting on the A7s mark I 😉 but I do still have a question: I still have problems with the sony getting the colors i want and reading the internet theres a million advice but they were not totally successful for me. here a beginners question i still have: shooting s-log2 means i HAVE TO use the s-gamut color mode to make sense of it , right? i heard things like using ITU etc but that didnt work for me… I get often best results with the camera in auto-white balance mode which leaves me suspicious if there is not a better way. I think the cam has a weird tendency for yellow and green in the skin tones and in all the mid range and sometimes it is very prominent and sometimes ok.. I would be pleased to know your take on that.. thank you!!!

    1. When shooting with S-Log if you wish to use LUTs or any other workflow designed for Log then you must use the correct matching colour gamut otherwise the colour may shift as brightness/exposure changes. Gamut and Gamma are designed to work as matched pairs.

      Regarding colour generally, with a Log workflow it all comes down to choices and decisions made during the grading process. It also depends on whether the grading software you are using is designed to work with Log. A lot of normal editing software was never designed to work with log and as a result it can be harder to get the look that you want. I was an Adobe Premiere user for decades but I really struggled to get the look and colours I really wanted from log and raw material. After switching to DaVinci Resolve all those issues went away as Resolve is designed to work with log and raw formats and it has the all the tools needed to create almost any look and colour palette you wish.

    2. Hi Kris, I definitely wouldn’t auto white balance with the Sony A7s II, I would white balance with a gray card and get it set properly.

      Make sure you’re over exposing by a couple of stops when you use s-log 2.

  94. hello Alister,

    got a question to bother you again. i noticed that you’ve mentioned that the middle gray point of s-log2 is 32%, and that of s-log3 is around 36%( i can’t remember the exact number),meanwhile i’ve learned that there’re different middle point value for different logs, such as c-log, v-log,etc.
    as a result, i’ve been wondering what is the function of these numbers to a cinematographer. just take s-log2 and s-log3 as examples: while shooting a footage, if i picked s-log2 rather than s-log3, does that mean i could get much more room in highlight part than that in s-log3? and should be more careful in dark parts.
    what’s more, in post production, since we’ve already known the exact value of the chosen log curve, does that mean it is necessary we should firstly check if the exposure is right at the exact middle gray point? ( to be exactly, the exact IRE values in color grading)

    best regards,


    1. The differing values are due to the different shape of the gamma curves. S-Log2 was specifically designed for use with video sensors so the placement of middle grey optimises the data distribution in the recording for an electronic camera. S-Log3, like C-Log, Log-C, V-Log is based on an old film curve called Cineon, so the values it uses are based on film levels and less optimum for a video camera but colourists used to working with Cineon prefer the familiarity that using a Cineon type curve brings.

      Middle grey always has the same relationship between black/white/highlights etc so using different curves with different middle grey values won’t in itself alter highlight or shadow range. Middle grey is an extremely useful exposure reference level as this is what most light meters are calibrated agains and it also tends to be the average brightness of a scene when all the levels are added together and an average value determined.

      1. Hi Alister,

        Thanks for your reply. so can i take it like this:

        actually, what the middle grey point shows is how much darker or brighter the chosen log or gamma curve would be like when exposing a grey card, comparing to exposing a grey card using rec 709. just like what you said about Hypergamma 1-8 in the FS7 video. the value in itself won’t do anything to altering highlight or shadow range because that’s what the dynamic range’s part.

        however, when we are exposing a grey card, we should take into consideration where the grey point is so we could know how much darkder it would be compared to rec 709, than we could choose to expose the card right to the grey point or darker or brighter, according to what kind of scene we want to create.

        another function of grey point of different logs , i guess, would be for us to chekc if we have exposed middle grey right. i mean, if the waveform shows that the line of the grey card is locating around the reference point, then it means we have exposured right under the chosen curve. and in color grading, when we are doing color correction, we could firstly tweak the grey card back to the reference grey point line to make sure the exposure is right.

        and i guess these are the main functions of the grey point of different curves?

        best regards,


  95. Hey Alister

    Im still a bit confused about the exposure levels. Im shooting slog 2 on a sony A7iii.

    1) What zebra settings should I use if im exposing to skintones?

    2) What settings for highlights such as the sky?

    I have seen around the internet that skintones should be 70% zebra and highlights 107% IRE.

    I hope you can help me.



    1. White caucasian Skin tones are generally half way between white and middle grey. For example, for Rec-709 middle grey is 45% and white is 90% so skin tones would be 68% (hence why the use of 70% zebras for Rec-709 is typical).

      S-Log2 middle grey is 32% and white is 59%, so normal skin tones would be a nominal 46%. This is with no exposure offset added.

      The A7SIII is a low noise camera, so there is no pressing need to add an exposure offset as with older and noisier cameras. However some people still prefer a better signal to noise ratio so may choose to offset the exposure somewhat brighter. Adding on more stop would put skin tones at approx 56%, adding 2 stops 68%.

      S-Log2 clips at 106%.

  96. Hello Alister,

    I’m trying to understand the dynamic range chart of my A7III with cine4 profile. I use Datacolor SpyderCheckr 24 for middle gray reference. I know that with cine4 profile, at 200 ISO, middle gray should be 33%. Exposure meter setting is spot standard mode. I set zebra value to 33% and adjust exposition until to view zebra bars on my viewfinder. The light meter of my camera shows 1+1/3 stops underexpose of middle gray. There is something of mistake ?

    Thanks a lot.

    Francesco G.

    1. To get more dynamic range and increase the highlight range you have to make room to record it. This is done by moving the midrange down. So the image will be darker than you would have with a curve with less dynamic range. Your skintones should be around 55-60% when correctly exposed

  97. hey Alister,
    one of the best articles iv read.
    just wanted to ask for your opinion –
    how would you approach bringing down the exposure in post?
    im using Resolve’s new HDR colorspace aware tools to set the gamma to slog2 and then lowering the exposure by 2 stops (which gives me exactly the same results as the -2 stops slog2 LUT from lutcalc), but I found out the Luma curve gives more saturated results.
    Is there a “correct” way?

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