Tag Archives: exposure

FX9 ISO Rating Confirmation Test

While I had the light meter and exposure test chart out for the FX6 I decided to do the same exposure level confirmation test for the FX9. No nasty surprises, the FX9’s ISO ratings certainly appear to be correct. Again using a DSC Labs exposure reference chart with 18% middle grey and 90% white plus my trusty Sekonic I tested the FX9 at both 800 ISO and 4000 ISO and my light meter and the camera were in good agreement. At 800 ISO the light meter was saying f4.01 while the camera was at f4, I suspect this tiny difference is probably down to transmission losses in the lens.

FX9-Exposure-Test-800_1.2.1 FX9 ISO Rating Confirmation Test
FX9 Exposure rating test at 800 ISO.
FX9-Exposure-Test-4000_1.1.1 FX9 ISO Rating Confirmation Test
FX9 Exposure ISO rating test at 4000 ISO.

FX6 ISO rating Confirmation Test

I have already done this a few times, but having seen some other tests suggesting the FX6’s ISO ratings were incorrect. So I decided to re-confirm my previous findings, which is that the ratings Sony give their cameras is correct. For the test I used a DSC labs exposure calibration chart which is an extremely accurate 18%/90% reflectivity chart and my trusty Sekonic light meter. As you can see at both 800 ISO and 12,800 ISO the light meters indicated exposure settings perfectly match the camera’s ISO ratings, shutter speed and aperture. For the 12,800 ISO test, as my light meter doesn’t go up to 12,800 ISO  I set the light meter to 6400 ISO which is one stop lower than the cameras 12,800. The light meter indicated f11 which is one stop below the f16 required by the camera – confirming that the ISO rating is correct.

FX6-Exposure-test-800_1.2.1 FX6 ISO rating Confirmation Test
800 ISO FX6 exposure calibration test.
FX6-Exposure-test-12800_1.1.2 FX6 ISO rating Confirmation Test
FX6 12,800 ISo exposure calibration test.

A Guide the the FX6’s CineEI Mode.

Mode-CineEI1_1.1.1-1024x576 A Guide the the FX6's CineEI Mode.
The FX6 CineEI mode can be enabled via status page 4 or via the main menu and project settings.

 

WHAT IS CINE EI?

The FX6’s CineEI mode is designed to make shooting using S-Log3 or raw easy and straightforward. It optimises the camera so that settings such as the recording ISO, noise reduction and sharpening are all optimised for recording either S-Log3 or raw with the best possible dynamic range.

Mode-CineEI2_1.1.1-600x338 A Guide the the FX6's CineEI Mode.

It also makes sure that the S-Log3 or raw recordings are optimised for grading. In addition you can use a LUT (Look Up Table) in the viewfinder or on the HDMI/SDI output to provide an approximation of how your footage will look after it’s been graded as well as to assist you in getting the exposure right.

HINT: What is a LUT? A LUT is a simple Look Up Table of input values that represent different levels in the recording format (in this case S-Log3) and then converts those input values to new output values that are appropriate for the monitor or display range you are using. This conversion can included stylised adjustments to give the output image a specific look.

Once you have a LUT enabled and you are viewing the LUT either in the viewfinder or on a monitor an exposure offset can be applied to the LUT to make it darker or brighter than normal. This LUT brightness offset is used to allow you to deliberately offset how bright the recordings are, this is the “EI” or Exposure Index part of CineEI. More on that later.

BUILT IN LUTS

The FX6 has 3 built in LUTs, but in addition to the built in LUTs you can load your own “user LUTs” into the camera as what the FX6 calls “Base Looks” making this a very flexible and capable system. If you want to load you own LUTs into the camera these must be 3D Cube LUT’s and should be placed in the — Private : SONY : PRO : LUT folder of an SD card or CFExpress card that has been formated in card slot 2 of the FX6.  The LUT’s should be 17x or preferably 33x cube LUT’s designed for use with S-Log3 and SGamut3.cine. They are loaded via the main menu PAINT – BASE LOOK page.

lut-selection_1.1.1-600x338 A Guide the the FX6's CineEI Mode.
The FX6 has 3 included LUT’s, these are s709, 709(800) and S-Log3. The AC-BCST LUT seen here is a user LUT that has been saved to the camera.

 

CODEC CHOICE.

As your material will require grading in post production, if you are shooting UHD or 4K you should NOT use XAVC-L because in UHD/4K XAVC-L is 8 bit 4:2:0. A much better choice is XAVC-I which is always 10 bit 4:2:2 and/or raw.

FIXED RECORDING ISO.

Once the camera is set to use the CineEI mode the recording sensitivity is fixed to either 800 ISO when in Lo Base sensitivity or 12,800 ISO when the camera is set to Hi Base sensitivity. These values cannot be changed and your recordings will always take place at one of these sensitivity levels.

ENABLE A LUT.

To take full advantage of the Cine EI mode the next step is to enable a LUT for the viewfinder and also optionally for the HDMI and SDI outputs.

SDI-MLUT-ON_1.1.10-600x338 A Guide the the FX6's CineEI Mode.
MLUT’s are enabled and disabled via status page 5 or in the main menu under Shooting – LUT NO/OFF

 

The default LUT is Sony’s s709 LUT. This is the same LUT as used by the Venice digital cinema camera. s709 is designed to be a starting point for a film style look. To achieve this film style look it uses brightness levels more commonly found in feature films rather than the levels normally used in the majority of regular TV shows.

selected-lut-status-pages_1.1.1-600x338 A Guide the the FX6's CineEI Mode.
The default LUT is s709. The LUT can be changed from Status Page 5 or in the main menu under PAINT – BASE LOOK – SELECT


LUT EXPOSURE LEVELS

There are some important things to understand about different LUTs and Base Looks. Each LUT/Look will have it’s own optimum brightness levels. They will not all be the same. Some will be brighter or darker than others when exposed correctly, so it’s vital that you understand what levels any LUT that you chose to use needs to be exposed at.

Another LUT that the FX6 includes is Sony’s 709(800) LUT. This LUT is more closely aligned with the levels used in normal TV productions, so it looks very different to s709 and has very different brightness levels when exposed correctly.

The chart below gives the “correct” exposure values for S-Log3 as well as some guide values based on my own measurements for the s709 and 709(800) LUTs in the FX6.

  Middle Grey Average Skin Tones 90% Reflectivity white card (add 2-3% for white paper).
S-Log3 41% 48-52% 61%
s709 44-45% 57-62% 77-78%
709(800) 44-45% 65-70% 89%

MEASURING THE EXPOSURE.

There are many ways to measure your exposure when shooting using S-Log3 and LUT’s. You could choose to use a light meter, in which case the light meter would be set to match the EI (Exposure Index) value set in the camera. You can just look at the image in the viewfinder and judge when it looks right. Most of the time this is OK, but it isn’t particularly accurate. My prefered method is to use a white card or grey card and then use the cameras built in video signal monitor and the waveform display to actually measure the brightness of the grey card or white card.

Video-Signal-Monitor-ON_1.1.5-600x338 A Guide the the FX6's CineEI Mode.
The waveform display is enabled in the menu under MONITORING – DISPLAY ON/OFF – VIDEO SIGNAL MONITOR


If you are not familiar with a waveform display it actually really easy to understand. The bottom of the waveform is black and the very top is 109%, the brightest that the camera can ever record to. The left hand side is the left of the video image and the right is the right of the video image. The thin reference lines across the waveform display are at 0% (the darkest a video image should ever normally be), 25%, 50%, 75% and 100%.

waveform-2 A Guide the the FX6's CineEI Mode.
The levels shown by the FX6’s waveform display


In addition the FX6’s waveform display includes 2 yellow lines. The position of these yellow lines is determined to the levels that the cameras zebras are set to. By default the lower yellow line will be at 70% to match Zebra 1 and the upper line at 100% to match zebra 2.

waveform-1 A Guide the the FX6's CineEI Mode.

MEASURING THE EXPOSURE.

The waveform display measures the signal that is on the HDMI and the SDI output. So once you have turned on the LUT for the HDMI/SDI it is the levels of the LUT that is being measured. What the waveform is measuring is indicated just above the waveform display.

To make it easier to understand how CineEI works and to show you how I like to have my FX6 setup, I find it easier to start off by turning OFF the LUT for the SDI and HDMI and measuring the exposure of the S-Log3. If you do this when the the Exposure Index (EI) is equal to the Recording or Base ISO then we can establish the correct exposure for the S-Log3 using a white card or white piece of paper and then also check the exposure of the LUT.

FIRST CHECK AND SET THE EXPOSURE INDEX LEVELS.

With the cameras base ISO set to low / 800 ISO I recommend that you set the EI levels in the main menu SHOOTING – ISO/Gain/EI as follows: 

EI-Levels_1.1.13-600x338 A Guide the the FX6's CineEI Mode.
My recommended exposure index levels of 800/400/200 EI

 

ISO/GAIN BUTTON:

When using the CineEI mode you can change the EI several ways. The most commonly used ways will likely be via the L/M/H ISO/Gain switch or by pressing the ISO/Gain button and then using the multi-function dial (MFD) to change the EI.  Do note that when you use the multi-function dial or Direct Menu to change the EI this new EI setting changes the preset value associated with the current position of the L/M/H switch.

I do not set an Exposure Index higher than the base recording ISO. The reason for this is that if you record using a high EI value your images will be noisy and grainy and could be very difficult to grade. Because you don’t ever see your final results until you get into post production, if you accidentally record noisy log you won’t really know how bad the footage will be until it is perhaps too late to do anything about it. So I set the EI for the Low Base 800 ISO as H>800EI,  M>400EI, L>200EI. The difference between each of these EI’s is one stop and that makes it easier when you are checking any exposure changes. 

For the 12,800 High base ISO I set the EI to H>12800EI, M>6400EI, L>3200EI.

FOR THIS EXAMPLE START AT LOW BASE/800 ISO and 800 EI.

By using the same EI as the base recording ISO there will be no offset or difference between the correct exposure for the LUT and the correct, or base exposure for the S-Log3. Expose the LUT corrrectly and the S-Log3 will be also be normally exposed. Expose the S-Log3 normally and the LUT will look correct.

FOR THIS EXAMPLE LET’S START WITH THE SDI/HDMI LUT OFF.

For this example I am going to start with the LUT OFF for the SDI and HDMI, this way the waveform display will be measuring the S-Log3. Just above the waveform it should say SG3C/Slog3, telling you the waveform is measuring the S-Log3. 

MLUT-VF-Only_1.1.8-600x338 A Guide the the FX6's CineEI Mode.
When the LUT (MLUT) is off for the SDI/HDM the waveform will be measuring the S-Log3 exposure level.

 

Referring to the table of exposure levels above we can see that the correct S-Log3 exposure for a white card (90% reflectivity white) is 61% – if using a normal piece of printer paper I suggest using a value a little higher (around 63%) as white paper tends to be a little brighter than a proper white test card.

SETTING ZEBRA 1 TO 61%

To make finding where 61% is on the waveform I recommend setting Zebra 1 to 61% so that the lower of the two yellow zebra lines is at 61%.

zebra1-61-1_1.1.8-600x338 A Guide the the FX6's CineEI Mode.
Set Zebra 1 to 61% via the main menu and MONITORING – ZEBRA.


So now when checking the exposure of a white card when the waveform is measuring the S-Log3 it is simply a case of adjusting the exposure until the white card is at the same level as the 61% line. Alternately you could use an 18% grey card, in which case you would set Zebra 1 to 41%, however there are often times when I forget my grey card but I almost always have a piece of paper somewhere.

white-card-at-61 A Guide the the FX6's CineEI Mode.
White target exposed at 61% when measuring the S-Log3

 

So now we know the S-Log3 is correctly exposed lets turn ON the LUT for the SDI and HDMI outputs and check the exposure level of the s709 LUT.

TURN ON THE LUT.

SDI-MLUT-ON_1.1.10-600x338 A Guide the the FX6's CineEI Mode.
MLUT’s are enabled and disabled via status page 5 or in the main menu under Shooting – LUT NO/OFF

 

And if we refer to the exposure chart given towards the top of the page we will see that white for the s709 LUT is 77%. So now let’s set Zebra 2 to 77% to make 77% easier to find on the waveform. Do remember however that other LUTs may need different levels, 77% is just for s709, 709(800) would require Zebra 2 to be set to 89%.

SET ZEBRA 2 TO 77% FOR s709

zebra2-77-2_1.1.12-600x338 A Guide the the FX6's CineEI Mode.
Set Zebra 2 to the correct white level for the LUT you are using via the main menu and MONITORING – ZEBRA.

 

Now with the LUT ON for the SDI/HDMI we should see the brightness of the white card line up with the upper yellow line that represents Zebra 2 and 77%.

s709-LUT-correct-version-2 A Guide the the FX6's CineEI Mode.

 

s709-77pc-zebra_1.1.13-600x338 A Guide the the FX6's CineEI Mode.

As you can see from the above example when the Base ISO and Exposure Index are matched, when the LUT for the SDI/HDMI is OFF and the white card is at 61% on the waveform the S-Log3 is correctly exposed.

Then when the s709 LUT is ON for the SDI/HDMI and the white card is at 77% we are correctly exposed. By having Zebra 1 set at 61% (for S-Log3) and Zebra 2 set for the white level for for your chosen LUT we can check either simply by turning the HDMI/SDI LUT ON or OFF.

USING THE 709(800) LUT INSTEAD

If you want a more contrasty looking image in the viewfinder and similar brightness levels to other video cameras – for example skin tones around 70% you might prefer to use the 709(800) LUT.  When using the 709(800) LUT to measure a white card you should set Zebra 2 to 89%. It’s also worth noting that with the 709(800) LUT, if you wish, you could just leave the zebras at their default settings with Zebra 1 at 70% where just like a conventional Rec-709 video camera they will appear over brighter skin tones when viewing via the LUT. 

709800-correct A Guide the the FX6's CineEI Mode.

CHANGING THE EXPOSURE INDEX TO OFFSET THE LOG EXPOSURE.

Sometimes it can be desirable to expose the S-Log3 a little brighter. For example when shooting scenes with a low average brightness level or scenes with large areas of shadows. The FX6 has very low noise levels at 800 ISO base. So for most scenes with higher average brightness levels there is no need to expose the log brighter. But there is a bit more noise at 12,800 ISO base. As a result it can be beneficial to expose the S-Log3 a bit brighter when using 12,800 ISO base.

The CineEI mode makes this very easy to do in a very controlled manner. Keeping the amount of over exposure constant helps speed up the grading process as all your material can be graded in exactly the same way.

Over exposing or underexposing Log does not change the captured dynamic range, it will always be the same. However exposing log brighter will reduce the highlight range while at the same time increasing the shadow range. A brighter exposure will result in less noise after grading.

Exposing log darker will increase the highlight range but decrease the shadow range. A darker exposure will result in more noise after grading. Because under exposed log can become very noisy, very quickly I do not recommend under exposing log,  because of this I strongly advise against ever using an EI that is higher than the base ISO as this will result in under exposed log.

CHANGING THE EI ONLY CHANGES THE LUT.

When you change the Exposure Index the only thing that actually changes is the brightness of the LUT. So for EI to work you must be monitoring via a LUT.

Below is what happens to the image in the viewfinder when you have a LUT enabled (s709 in this case) and you lower the EI from 800 EI down to 200 EI in 1 stop steps and make no changes to the exposure.

s709-CORRECT2_1.1.24-600x338 A Guide the the FX6's CineEI Mode.
s709 at 800 EI and correctly exposed – note aperture is f8.
s709-400EI-2_1.1.23-600x338 A Guide the the FX6's CineEI Mode.
s709 with the EI set one stop lower at 400 EI but no change to the exposure made, aperture is still f8.
s709-200EI-2_1.1.24-600x338 A Guide the the FX6's CineEI Mode.
s709 now 2 stops darker at 200EI – no change to exposure, aperture is still f8

 

As we have not changed the exposure in any way, the only thing changing is the brightness of the LUT. The recording levels have not yet changed in any way.

BUT NOW WE CHANGE THE EXPOSURE

Because the image in the viewfinder is now dark and the white card no longer reaches the correct exposure for the LUT, we now adjust the exposure. In this example I simply opened the aperture by 2 stops from f8 to f4 to match the 2 stop change in the LUT brightness. Now the image in the viewfinder looks correct again and the white card is meeting the upper yellow line again (77% as set by Zebra 2 level).

s709-200EI-Corrected_1.1.25-600x338 A Guide the the FX6's CineEI Mode.
The EI is at 200 but now the aperture has been opened by 2 stops to f4 so now the LUT is exposed correctly again.

 

BECAUSE THE EXPOSURE IS BRIGHTER THE S-LOG3 IS NOW ALSO BRIGHTER.

Because I have opened the aperture by 2 stops to make the 200 EI LUT exposure look right the S-Log3 recordings will now be 2 stops brighter. If I turn off the LUT for the SDI/HDMI we can see that the S-Log3 is much brighter 2 stops brighter like this, the S-log3 white card level becomes 79%, so it appears slightly above the 77% Zebra 1 line.

s-log3-200ei-corrected_1.1.26-600x338 A Guide the the FX6's CineEI Mode.
After increasing the exposure by 2 stops to compensate for the 2 stop darker LUT (200EI) the S-Log3 recordings become 2 stops brighter and the S-Log3 white card level becomes approx 79%

 

Buy making the LUT darker by 2 stops, then adjusting the exposure upwards 2 stops to return the LUT to the original brightness we have made our recordings 2 stops brighter. This is how you use CineEI to alter the brightness of your recordings.

At Low base ISO (800 ISO) the FX6 is a low noise camera, so there is no need to routinely over expose the log as there is with more noisy cameras like the FS5 or FS7. So I normally shoot at 800 EI. When using the high base ISO or 12,800 ISO there is a bit more noise and when using high base I will typically set the EI to 6400 EI as the 1 stop brighter recordings that this will result in helps compensate for the increased recording noise.

In the examples given here I have used a white card to set the exposure. This is accurate and highly repeatable. But there will be times where you may not have a white card. At these times CineEI can still be used either by setting the Zebras to the appropriate skin tone levels for the chosen LUT (see the table towards the beginning) or by carefully “eyeballing” the brightness of the LUT image – if it looks right, it probably is right. If you are eyeballing it I highly recommend a deep sunshade or other device to exclude as much light as possible from the viewfinder.

You can also use any user LUTs that you have loaded into the camera to alter the base look when you are shooting in custom mode. For more information on that please watch the video below.

PXW-FX9 Exposure Accuracy – Can I use A Light Meter?

This came up during a Facebook discussion. Can you use a light meter with the FX9 and will the exposure be correct?

When I first met the FX9 at Sony’s Pinewood Studios facility we tested and checked all sorts of different aspects of the cameras performance against various light meters and test charts. I found that the camera matched what we expected perfectly well.

But just to be sure I have just tested my own example against my trusty Sekonic light meter and once again I am happy to say that everything seems to match as expected.

In this simple setup I used a couple of different charts with middle grey and 90% white – I do find that there is some variation between charts in how reflective the 90% and 18% reflectivity areas are. So I’ve used a couple here and my main reference is the large DSC Labs white and middle grey chart.

I used the dimmers on my lights so that my metered exposure reading for 24fps 1/48th shutter came to exactly f5.6. Then I set the lens to f5.6 (Sony 24-70mm GMaster).

The result is pretty much as close to a perfect exposure as one can expect. So don’t be afraid to use a light meter with the FX9.

Screenshot-2020-07-21-at-10.11.45 PXW-FX9 Exposure Accuracy - Can I use A Light Meter?
Exposed via the light meter, screen grab from Catalyst Browse.

 

Screenshot-2020-07-21-at-10.14.53 PXW-FX9 Exposure Accuracy - Can I use A Light Meter?
And the levels as measured in DaVinci Resolve. All looks good and where you would expect S-Log3 to be.

Shooting S-Log3 on the PXW-FX9 – Do I need to expose bright?

Having shot quite a bit of S-Log3 content on the new Sony PXW-FX9 I thought I would comment on my exposure preferences. When shooting with an FS5, FS7 or F5, which all use the same earlier generation 4K sensor I find that to get the best results I need to expose between 1 and 2 stops brighter than the 41% for middle grey that Sony recommend. This is because I find my footage to be noisier than I would like if I don’t expose brighter. So when using CineEI on these cameras I use 800EI instead of the base 2000EI

However the FX9 uses a newer state of the art back illuminated sensor. This more sensitive sensor produces less noise so with the FX9 I no longer feel it is necessary to expose more brightly than the base exposure – at either of the base ISO’s. So if I am shooting using CineEI and 800 base, I use 800EI. When shooting at 4000 base, I use 4000 EI. 

This makes life so much easier. It also means that if you are shooting in a mode where LUT’s are not available (such as 120fps HD) then you can use the included viewfinder gamma assist function instead. Viewfinder gamma assist adds the same 709(800) look to the viewfinder as you would get from using the cameras built in 709(800) LUT.  You can use the VF gamma assist to help judge your exposure just as you would with a LUT.  Basically, if it looks right in the viewfinder, it almost certainly is right.

Testing various FX9’s against my Sekonic light meter the cameras CineEI ISO ratings seem to be spot on. So I would have no concerns if using a light meter to expose.  The camera also has a waveform scope and zebras to help guide your exposure.

VF Gamma assist is available in all modes on the FX9, including playback. Just be careful that you don’t have both a LUT on and gamma assist at the same time.

ISO and EI – using the right terms makes what you are doing easier to understand.

ISO and EI are different things and have different meanings. I find that it really helps understand what you are doing if you use the terms correctly and understand exactly what each really means.

ISO is the measured sensitivity of film stock. There is no actual direct equivalent for electronic cameras as the camera manufacturer is free to determine what they believe is an acceptable noise level. So one camera with an ISO of 1000 may be a lot more or less sensitive than another camera rated at 1000 ISO, it all depends on how much noise the manufacturer things is acceptable for that particular camera.

Broadly speaking on an electronic camera ISO is the number you would enter in to a light meter to achieve the a normally exposed image. It is the nearest equivalent to a sensitivity rating, it isn’t an actual sensitivity rating, but it’s what you need to enter into a light meter if you want to set the exposure that way.

EI is the Exposure Index. For film this is the manufacturers recommended best setting for your light meter to get the best results following the standard developing process for the chosen film stock. It is often different from the films true sensitivity rating. For example Kodak 500T is a 500 ISO film stock that has an EI of 350 when shooting under tungsten light. In almost all situations you would use the EI and not the ISO.

On an electronic camera EI normally refers to an exposure rating that you have chosen to give the camera to get the optimum results for the type of scene you are shooting. ISO may give the median/average/typical exposure for the camera but often rating the camera at a different ISO can give better results depending on your preferences for noise or highlight/shadow range etc. If you find exposing a bit brighter helps your images then you are rating the camera slower (treating it as though it’s less sensitive) and you would enter your new lower sensitivity rating into your light meter and this would be the EI.

Keeping EI and ISO as two different things (because they are) helps you to understand what your camera is doing. ISO is the base or manufacturer sensitivity rating and in most (but not all) log or raw cameras you cannot change this.

EI is the equivalent sensitivity number that you may choose to use to offset the exposure away from the manufacturers rating.

If you freely interchange ISO and EI it’s very confusing for people as they don’t know whether you are referring to the base sensitivity rating or a sensitivity rating that is not the base sensitivity but actually some kind of offset.

If you have a camera with an ISO rating of 2000 and you say “I’m shooting at 800 EI” then it’s clear that you are using a 1.3 stop exposure offset. But if you just say “I’m shooting at 800 ISO” it is less clear as to exactly what you are doing. Have you somehow changed the cameras base sensitivity or are you using an offset? While the numbers used by EI and ISO are the same, the meaning of the terms ISO and EI are importantly different.

Noise, ISO, Gain, S-Log2 v S-Log3 and exposure.

Even though I have written about these many times before the message still just doesn’t seem to be getting through to people.

Since the dawn of photography and video the only way to really change the signal to noise ratio and ultimately how noisy the pictures are is by changing how much light you put onto the sensor.

Gain, gamma, log, raw, etc etc only have a minimal effect on the signal to noise ratio. Modern cameras do admittedly employ a lot of noise reduction processes to help combat high noise levels, but these come at a price. Typically they soften the image or introduce artefacts such as banding, smear or edge tearing. So you always want to start off with the best possible image from the sensor with the least possible noise and the only way to achieve that is through good exposure – putting the optimum amount of light onto the sensor.

ISO is so confusing:

But just to confuse things the use of ISO to rate an electronic cameras sensitivity has become normal. But the problem is that most people have no clue about what this really means. On an electronic camera ISO is NOT a sensitivity measurement, it is nothing more than a number that you can put into an external light meter to allow you to use that light meter to obtain settings for the shutter speed and aperture that will give you the camera manufacturers suggest optimum exposure. That’s it – and that is very different to sensitivity.

Lets take Sony’s FS7 as an example (most other cameras behave in a very similar way).

If you set the FS7 up at 0dB gain, rec-709, it will have an exposure rating of 800 ISO. Use a light meter to expose with the meters ISO dial set to 800. Lets say the light meter says set the aperture to f8. When you do this the image is correctly exposed, looks good (well as good as 709 gets at least) and for most people has a perfectly acceptable amount of noise.

Now switch the camera to S-Log2 or S-Log3. With the camera still set to 0dB the ISO rating changes to 2000 which give the impression that the camera may have become more sensitive. But did we change the sensor? No.  Have we added any more gain? No, we have not, the camera is still at 0dB. But if you now expose at the recommended levels, after you have done your grading and you grade to levels similar to 709 the pictures will look quite a lot noisier than pictures shot using Rec-709.

So what’s going on?

If you now go back to the light meter to expose the very same scene, you turn the ISO dial on the light meter from 800 to 2000 ISO and the light meter will tell you to now set the aperture to f13 (approx). So starting at the f8 you had for 800 ISO, you close the aperture on the camera by 1.3 stops to f13 and you will have the “correct” exposure.

BUT: now you are putting 1.3 stops less light on to the sensor so the signal coming from the sensor is reduced by 9dB and as a result the sensor noise that is always there and never really changes is much more noticeable. As a result compared to 709 the graded S-Log looks noisy and it looks noisier by the equivalent of 9dB. This is not because you have changed the cameras sensitivity or changed because you have changed the amount of camera gain but because compared to when you shoot in 709 the sensor is being under exposed and as a result it is outputting a signal 9dB lower. So in post production when you grade or add a LUT you have to add 9dB of gain to get the same brightness as the original direct rec-709 recording and as well as making the desirable image brighter it also makes the noise 9dB higher (unless you do some very fancy noise reduction work in post).

So what do you do?

It’s common simply to open the aperture back up again, typically by 1.5 stops so that after post production grading the S-log looks no more noisy than the 709 from the FS7 – Because in reality the FS7’s sensor works best for most people when rated at the equivalent of 800 ISO rather than 2000 – probably because it’s real sensitivity is 800 ISO.

When you think about it, when you shoot with Rec-709 or some other gamma that won’t be graded it’s important that it looks good right out of the camera. So the camera manufacturer will ensure that the rec-709 noise and grain v sensitivity settings are optimum – so this is probably the optimum ISO rating for the camera in terms of noise, grain and sensitivity.

So don’t be fooled into thinking that the FS7 is more sensitive when shooting with log, because it isn’t. The only reason the ISO rating goes up as it does is so that if you were using a light meter it would make you put less light onto the sensor which then allows the sensor to handle a brighter highlight range. But of course if you put less light onto the sensor the sensor won’t be able to see so far into the shadows and the picture may be noisy which limits still further the use of any shadow information. So it’s a trade-off, more highlights but less shadows and more noise. But the sensitivity is actually the same. Its’s an exposure change not a sensitivity change.

So then we get into the S-Log2 or S-Log3 debate.

First of all lets just be absolutely clear that both have exactly the same highlight and shadow ranges. Both go to +6 stops and -8 stops, there is no difference in that regard. Period.

And lets also be very clear that both have exactly the same signal to noise ratios. S-log3 is NOT noisier than S-log2. S-log 3 records some of the mid range using higher code values than S-Log2 and before you grade it that can sometimes make it appear like it’s noisier, but the reality is, it is not noisier.  Just like the differing ISO ratings for different gamma curves, this isn’t a sensitivity change, it’s just different code values being used. See this article if you want the hard proof: http://www.xdcam-user.com/2014/03/understanding-sonys-slog3-it-isnt-really-noisy/

Don’t forget when you shoot with log you will be grading the image. So you will be adjusting the brightness of the image. If you grade S-Log2 and S-Log3 to the same brightness levels the cumulative gain (the gain added in camera and the gain added in post) ends up the same. So it doesn’t matter which you use in low light the final image, assuming a like for like grade will have the same amount of noise.

For 8 bit records S-Log2 has different benefits.

S-Log2 was designed from the outset for recording 14 stops with an electronic video camera. So it makes use of the cameras full recording range. S-Log3 is based on an old film log curve (cineon) designed to transfer 16 stops or more to a digital intermediate. So when the camera only has a 14 stop sensor you waste a large part of the available recording range. On a 10 bit camera this doesn’t make much difference. But on a 8 bit camera where you are already very limited with the number of tonal values you can record it isn’t ideal and as a result S-Log2 is often a better choice.

But if I shoot raw it’s all going to be so much better – isn’t it?

Yes, no, maybe…. For a start there are lot’s of different types of raw. There is linear raw, log raw, 10 bit log raw, 12 bit linear, 16 bit linear and they are all quite different.

But they are all limited by what the sensor can see and how noisy the sensor is. So raw won’t give you less noise (it might give different looking noise). Raw won’t give you a bigger dynamic range so it won’t allow you to capture deeper or brighter highlights.

But what raw does normally is to give you more data and normally less compression than the cameras internal recordings. In the case of Sony’s FS5 the internal UHD recordings are 8 bit and highly compressed while the raw output is 12 bit, that’s a 4 fold increase in the amount of tonal values. You can record the 12bit raw using uncompressed cDNG or Apples new ProResRaw codec which doesn’t introduce any appreciable compression artefacts and as a result the footage is much more flexible in post production. Go up to the Sony Venice, F5 or F55 cameras and you have 16 bit raw and X-OCN (which behaves exactly like raw) which has an absolutely incredible range of tonal values and is a real pleasure to work with in post production. But even with the Venice camera the raw does not have more dynamic range than the log. However because there are far more tonal values in the raw and X-OCN you can do more with it and it will hold up much better to aggressive grading.

It’s all about how you expose.

At the end of the day with all of these camera and formats how you expose is the limiting factor. A badly exposed Sony Venice probably won’t end up looking anywhere near as good as a well exposed FS7. A badly exposed FS7 won’t look as good as a well exposed FS5. No camera looks good when it isn’t exposed well.

Exposure isn’t brightness. You can add gain to make a picture brighter, you can also change the gamma curve to change how bright it is.  But these are not exposure changes. Exposure is all about putting the optimum amount of light onto the sensor. Enough light to produce a signal from the sensor that will overcome the sensors noise. But also not so much light that the sensor overloads. That’s what good exposure is. Fiddling around with gamma curves and gain settings will only every make a relatively small difference to noise levels compared to good exposure. There’s just no substitute for faster lenses, reflectors or actually adding light if you want clean images.

And don’t be fooled by ISO ratings. They don’t tell you how noisy the picture is going to be, they don’t tell you what the sensitivity is or even if it’s actually changing. All it tells you is what to set a light meter to.

Log and Raw Don’t have highlight a highlight roll off.

This just keeps coming up over and over. Almost all log gamma curves and the majority of raw recording formats don’t have a highlight roll-off. Any roll off that you might see is probably in the LUT’s that you are using.

The whole point of log and raw is to capture as much information about the scene that you are shooing as you can. Log normally achieves this by recording every stop above middle grey with a constant amount of data, so even the very brightest stop has the same amount of recording data as the ones below it – there is no roll off.

In conventional limited range recordings such as Rec-709, hypergamma, cinegamma etc, highlight roll-offs work by reducing the contrast in the highlights to make the amount of data needed to record the very brightest stops much smaller than used for the rest of the image. This allows 2 or 3 stops to be squeezed into a very small recording range, keeping most of the recording data available for a nice bright high contrast image. The reduction in contrast in the extreme highlights helps hide any highlight handling problems and makes it appear as though the sensors clipping point is reach in a more pleasing soft manner.

But you don’t want this in a log or raw recording as it makes grading much harder as the footage will contain different contrast ranges, each needing it’s own grading adjustments. Also by reducing contrast in the highlights you are reducing the data. It would be very difficult to un-pick a highlight roll off and if you did want to expand the data back out you will get issues such as banding.

S-log-levels Log and Raw Don't have highlight a highlight roll off.
Chart showing S-Log2 and S-Log3 plotted against f-stops and code values. Note how little data there is for each of the darker stops, the best data is above middle grey and there is no highlight roll-off. Note that current sensor only go to +6 stops over middle grey so S-Log2 and S-Log record to different peak levels.

S-Log2 and S-Log3 like almost all log gammas have no highlight roll-off. The only roll off is from middle grey and down. So if you underexpose you will start to roll away the data in your scenes mid range and that’s not good. Expose for the mid range, this is the most important part of any image. If your highlights are a bit clipped don’t worry about this too much. In post production you can add a roll off in the grade that will make any clipped highlights roll away gently. Adding a bit of highlight diffusion in post will also nicely mask any clipped highlights and make them look natural.

Firmware 4.30/1.20 for the PXW-FS7 and PXW-FS7M2 Released. New ISO change in Cine-EI added.

Sony have just released a firmware update for the PXW-FS7 and PXW-FS7 II cameras. This is a minor update with only one new feature being added which is the ability to alter the recorded ISO when shooting in the Cine-EI mode.

FS7: https://pro.sony/ue_US/support/software/pxw-fs7-software-v4-30

FS7 II: https://pro.sony/ue_US/support/software/pxw-fs7m2-v120

When the camera is set to CineEI, this new function is turned on and off in the menu under System – Base Settings – Rec/Out EI Applied.

What does it do?

When shooting normally using Cine EI, assuming that no LUT is applied to SDI1/Rec the camera always records at it’s base sensitivity (2000 ISO exposure rating) with no added gain. This is done to ensure that the cameras full dynamic range is always available and that the full recording range of either S-Log2 or S-Log3 is always available.

Then the EI system is used to apply a LUT just to the viewfinder or SDI 2 for monitoring. The gain of the LUT can then be changed to provide a brighter or darker viewfinder/monitor image. For example setting the EI to 1000 EI would make the viewfinder image darker than the base setting of 2000EI by 1 stop.

VF-side-by-side Firmware 4.30/1.20 for the PXW-FS7 and PXW-FS7M2 Released. New ISO change in Cine-EI added.
2000EI and 1000EI as seen in the viewfinder with NO exposure change (image from PMW-F5, but the FS7 is more or less the same).

Because you are viewing this darker image you would then open the cameras aperture by 1 stop to compensate. Opening the aperture up results in a brighter recording. A brighter recording, achieved by putting more light onto the sensor will have less noise than a darker exposure, so the end result is brighter recorded images with less noise.

This process is often referred to as “rating” the camera and it is in many cases preferable to “rate” the FS7 around a stop slower (Viewfinder is darker, less sensitive, so that means you end up opening up the aperture) than the base 2000 ISO rating to gain a cleaner image that typically gives much greater flexibility in post production. So many users will set the EI on an FS7 to 1000 or 800 (It’s no co-incidence that I find  get the sweet spot to be 800EI which happens to match the rating that Sony give the FS7 when shooting Rec-709).

Because in the normal EI mode there is no change to the cameras actual recording gain (the recordings take place at the equivalent of 2000 ISO) there is no change to the dynamic range. The camera will always capture 14 stops no matter what you set the EI to. However if you open the aperture by an extra stop (selecting 1000 EI, which results in a 1 stop darker viewfinder image, so to compensate you open up 1 stop) you move the mid point of the exposure up 1 stop. This means you will reduce the over exposure headroom by 1 stop but at the same time you gain one stop of under exposure range. You will see 1 stop further into the shadows, plus there will be less noise, so the shadow range becomes much more useable.

Conventional EI mode and Post Production.

In post production these brightly exposed images will need some degree of adjustment. If you are doing a virgin grade from scratch then you don’t really need to do anything extra or different, you will just grade it to taste.

If you are using a LUT you will need to either use an exposure compensated LUT (I always provide these in any of my free LUT sets) or you will need to correct the exposure before applying the LUT. If you apply a standard LUT and then try to correct the exposure the results will often not be satisfactory as the LUT determines many things such as where any highlight roll-off occurs. Correcting after this can result in washed out of flat looking skin tones. So really you need to make the exposure correction to the material before it is passed to the LUT.

No loss of dynamic range with conventional EI.

It’s worth noting that even though the levels are reduced to “normal” levels when applying an exposure compensated LUT or through grading this should not reduce the dynamic range. You do not just shift the range down (which would hard clip the blacks and cause a loss of DR at the low end). What you are typically doing is reducing the gain to bring the levels down and this allows the information in the new extended shadow range to be retained, so nothing is lost and your footage will still have 14 stops of DR along with nice clean shadows and mid tones.

Is this all too difficult?

However, some people find that the need to correct the exposure prior to adding the LUT difficult or time consuming (I don’t know why, they just do. It takes  no longer to add a compensated LUT than a normal LUT). Or some people find it difficult to get a good looking image from  brightly exposed footage (probably because they are grading after the LUT has been applied). For these reasons Sony have added the ability to bake the EI change directly into the recording by shifting the gain of the recordings to match the selected EI.

Rec/Out EI Applied:

So now if you enable Rec/Out EI Applied any change you make to the cameras EI settings will now also be applied as a gain change to the recordings. If you set the EI to 1000, then the recordings will take place at 1000 ISO and not 2000 ISO. This means that you do not have to make any exposure corrections in post production, just apply a standard LUT.

You will loose some of your dynamic range:

The down side to this is that you are now changing the gain of the camera. Changing the gain away from 0dB will reduce the dynamic range and affect the recording range. So, for example if you wish to shoot at 1000 EI have Rec/Out EI Applied you will be recording with -6dB gain and an effective ISO of 1000. You will have 1 stop less of shadow range as the cameras effective sensitivity is being reduced by 1 stop but the sensors clip/overload point remains the same. So when you open the aperture to compensate for the lower sensitivity you will have the same shadow range as base, but loose one stop off the top. The images will have less noise, but there will be no additional shadow information and a reduction in highlight range by 1 stop, the DR will be 13 stops.

Another side effect of this is that the peak recording level is also reduced. This is because the cameras clipping point is determined by the sensor. This sensor clip point is normally mapped to the peak recording level and the cameras noise floor is mapped to the black level (you can’t see things that are darker than the sensors noise floor no matter what level of gain you use as the noise will always be higher than the object brightness).

Slide2-1 Firmware 4.30/1.20 for the PXW-FS7 and PXW-FS7M2 Released. New ISO change in Cine-EI added.If you reduce the gain of the signal this level must decrease as a result. This means that S-Log3 which normally gets to around ~94% will now only reach ~85%, the change to S-Log2 is even greater (S-Log3’s peak recording level will reduce by 8.9% for every stop down you go, S-Log2 will reduce by 12% for each stop you go down ).

Slide6-1 Firmware 4.30/1.20 for the PXW-FS7 and PXW-FS7M2 Released. New ISO change in Cine-EI added.

 

Raising the EI/ISO will also reduce the dynamic range as the gain is applied after the sensor. So the sensors clip point remains the same, so the brightest highlight it handles remains fixed. Adding gain after this simply means the recordings will clip earlier, but you will get a brighter mid range, brighter (but not more) shadows and a noisier picture.

Slide4-1 Firmware 4.30/1.20 for the PXW-FS7 and PXW-FS7M2 Released. New ISO change in Cine-EI added.

 

What happens in post with Rec/Out EI Applied?

In post production these range and peak level changes mean that while a standard LUT will result in a correct looking mid range (because middle grey and skin tones will be at “normal” levels) there may be some problems with highlights never reaching 100% in the case of a low EI/ISO. Or being excessively clipped in the case of a high EI/ISO.  Remember LUT’s are designed to work over very specific ranges. So if the input to the LUT doesn’t reach the peak level the LUT is expecting then the output from the LUT will also be reduced. So often there will still be the need to do some additional grading of highlights prior to the application of the LUT, or the need to use LUT’s designed specifically for each ISO rating (and the design of these LUT’s is more complex than a simple exposure offset).

Is it really easier?

So while this new feature will simplify the workflow for some situations where an alternate ISO/EI has been used – because exposure correction in post production won’t be needed. It may actually make things more difficult if you have bright highlights or need to be sure that your finished video meets expected standards where highlights are at 100%. You will still need to do some grading.

I don’t recommend that you use it.

Personally I do not recommend that you use this new feature. There are plenty of exposure compensated LUT’s available online (I have lots here). Tweaking the exposure of log footage in post production isn’t that difficult, especially if you use a color managed workflow. My guess is that this is aimed at FCP-X users where FCP-X applies a default LUT as standard. In this instance footage shoot with an offset exposure will look over/under exposed while footage shoot with the EI/ISO Applied will look normal (except for the highlights). So on the face of things the workflow may appear simpler. But you are loosing dynamic range and surely the primary reason for shooting with log is to maximise the dynamic range and gain the greatest possible post production flexibility.  This new feature reduces dynamic range and as a result reduces post production flexibility.

Of course just because I don’t recommend it’s use, it doesn’t mean that you can’t or shouldn’t use it if it works for you, just make sure you fully understand what it is doing.

Beware the LC709 LUT double exposure offset.

The use o f the LC709 Type A LUT in Sony’s Cinealta cameras such as the PXW-FS7 or PMW-F55 is very common. This LUT is popular because it was designed to mimic the Arri cameras when in their Rec-709 mode. But before rushing out to use this LUT and any of the other LC709 series of LUT’s there are some things to consider.

The Arri cameras are rarely used in Rec-709 mode for anything other than quick turn around TV. You certainly wouldn’t normally record this for any feature or drama productions. It isn’t the “Arri Look” The Arri look normally comes as a result of shooting using Arri’s LogC and then grading that to get the look you want. The reason it exists is to provide a viewable image on set. It has more contrast than LogC and uses Rec 709 color primaries so the colors look right, but it isn’t Rec-709. It squeezes almost all of the cameras capture range into a something that can be viewed on a 709 monitor so it looks quite flat.

Because a very large dynamic range is being squeezed into a range suitable to be viewed on a regular, standard dynamic range monitor the white level is much reduced compared to regular Rec-709. In fact, white (such as a white piece of paper) should be exposed at around 70%. Skin tones should be exposed at around 55-60%.

If you are shooting S-Log on a Sony camera and using this LUT to monitor, if you were to expose using conventional levels, white at 85-90% skin tones at 65-70%, then you will be offsetting your exposure by around +1.5 stops. On it’s own this isn’t typically going to be a problem. In fact I often come across people that tell me that they always shoot at the cameras native EI using this LUT and get great, low noise pictures. When I dig a little deeper I often find that they are exposing white at 85% via the LC709 LUT. So in reality they are actually shooting with an exposure the equivalent of +1 to +1.5 stops over the base level.

Where you can really run into problems is when you have already added an exposure offset. Perhaps you are shooting on an FS7 where the native ISO is 2000 ISO and using an EI of 800. This is a little over a +1 stop exposure offset. Then if you use one of the LC709 LUT’s and expose the LUT so white is at 90% and skin tones at 70% you are adding another +1.5 stops to the exposure, so your total exposure offset is approaching 3 stops. This large an offset is rarely necessary and can be tricky to deal with in post. It’s also going to impact your highlight range.

So just be aware that different LUT’s require different white and grey levels and make sure you are exposing the LUT at it’s correct level so that you are not adding an additional offset to your desired exposure.