This is a question that comes up time and time again. I’ve been using the F5 and FS7 for almost 5 years. What I’ve discovered in that time is that the one thing that people notice more than anything from these cameras is noise if you get your exposure wrong. In addition it’s much harder to grade a noisy image than a clean one.
Lets take a look at a few key things about how we expose and how the F5/FS7 works (note the same principle applies to most log based cameras, the FS5 also benefits from being exposed brighter than the suggested base settings).
What in the image is important? What will your audience notice first? Mid-range, shadows or highlights?
I would suggest that most audiences first look at the mid range – faces, skin tones, building walls, plants etc. Next they will notice noise and grain or perhaps poor, muddy or murky shadows. The last thing they will notice is a few very brightly highlights such as specular reflections that might be clipped.
The old notion of protecting the highlights comes from traditional gamma curves with a knee or highlight roll off where everything brighter than a piece of white paper (90% white) is compressed into a very small recording range. As a result when shooting with conventional gamma curves ALL of the brighter parts of the image are compromised to some degree, typically showing a lack of contrast and texture, often showing some weird monotone colors. Log is not like that, there is no highlight roll off, so those brighter than white highlights are not compromised in the same way.
In the standard gammas at 0dB the PXW-FS7, like the PMW-F5 is rated at 800 ISO. This gives a good balance between noise and sensitivity. Footage shoot at 0dB/800ISO with the standard gammas or Hypergammas generally looks nice and clean with no obvious noise problems. However when we switch to log the native ISO rating of the cameras becomes 2000 ISO, so to expose “correctly” we need to stop the aperture down by 1.3 stops. This means that compared to 709 and HG1 to HG4, the sensor is being under exposed by 1.3 stops. Less light on the sensor will mean more noise in the final image. 1.3 stops is the equivalent of 9dB. Imagine how Rec709 looks if it is under exposed by 1.3 stops or has to have +9dB of gain added in. Well – thats what log at 2000 ISO will look like.
However log has lots of spare headroom and no highlight compression. So we can choose to expose brighter than the base ISO because pushing that white piece of paper brighter in exposure does not cause it to become compressed.
If you open the aperture back up by 1.3 stops you get back to where you would be with 709 in terms of noise and grain. This would be “rating” the camera at 800 ISO or using 800 EI. Rating the camera at 800EI you still have 4.7 stops of over exposure range, so the only things that will be clipped will in most cases be specular reflections or extreme highlights. There is no TV or monitor in existence that can show these properly, so no matter what you do, they will never be true to life. So don’t worry if you have some clipped highlights, ignore them. Bringing your exposure down to protect these is going to compromise the mid range and they will never look great anyway.
You should also be extremely cautious about ever using an EI higher that 2000. The camera is not becoming more sensitive, people are often misslead by high EI’s into thinking somehow they are capturing more than they really are. If you were to shoot at 4000 EI you will end up with footage 15dB noisier than if you were shooting the same scene using 709 at 800 ISO. That’s a lot of extra noise and you won’t necessarily appreciate just how noisy the footage will be while shooting looking at a small monitor or viewfinder.
I’ve been shooting with the F5 and then the FS7 for almost 5 years and I’ve never found a situation where I going to an EI higher than 800 would have resulted in a better end result. At the same time I’ve seen a lot of 2000 EI footage where noise in the mid range has been an issue, one particular example springs to mind of a high end car shoot where 2000 EI was used but the gloss and shine of the car bodywork is spoilt because it’s noisy, especially the darker coloured cars.
Of course this is just my opinion, based on my own experience, others may differ and the best thing you can do is test for yourself.
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Hi dear alister, when we use CINE EI and slog3 native iso is 2000 and does not change as you mentioned before, here you suggest to use 800 iso, what dose it mean in CINE EI mode and slog3 ?
I think he means that in Cine EI mode the native ISO cannot be changed from 2,000, so when he speaks of rating the camera at 800 ISO, what he means is that he is rating the Monitor LUT at 800 with a what-you-see-is-what-you-get image. If the ViewFinder image at 800 ISO looks under or over exposed, then he adjusts the aperture on the camera until the exposure looks right in the VF. In terms of Custom Mode, where the Standard and Hypergammas have a base ISO of 800, I think he is saying that the have a better signal to noise ratio and a cleaner image. But if, in Custom Mode, you switched the gamma from Standard or Hypergamma to SLOG, then your ISO will jump to 2,000 and appear over-exposed on the VF. To make it look properly exposed on the ViewFinder and I think that’s why he has correctly in quotes, you’d have to bring the aperture down. Unfortunately, MLUTs cannot be used in Custom Mode, when using Slog, I guess you are in a bit of pickle when trying to assess exposure from the VF alone. But that’s just what I get from reading it.
As per the page title – I use 800 EI.
Long time reader, first time commenter 🙂 In an earlier post, you mentioned rating the FS7 at EI 1000 when using slog3. That is what I’ve been doing for the past year and a half, as I’m not a big fan of the look of Sony’s standard gammas. Is there any appreciable difference between exposing at EI 800 vs EI 1000? I was always under the assumption that EI 1000 was equivalent to 0 DB on the FS7.
You have been fooled and confused by the way ISO works on an electronic camera. When shooting log on the FS7 0db results in an exposure rating of 2000ISO for S-log and 800ISO for 709. So when you use S-Log rated at 2000ISO your aperture will be 1.3 stops more closed than it would be when shooting Rec-709 when you are exposed at the nominal base “correct” exposure. This means the S-Log after grading will be 1.3 stops noisier than the 709 as the sensor is under exposed relative to the 709. By “rating” the camera at 800EI you open the aperture back up to the same aperture you would have in 709 and as a result the noise remains the same.
Thank you Alister, very informative.
As you’d expect I’ve found that 500 EI is cleaner than 800 EI but you either need to give the scene more light (sometimes difficult) or deal with an even shallower depth of field (sometimes too shallow)
Do you ever find yourself rating your camera at an EI lower than 800? In what circumstances would you do this?
Thanks
Ed
If I’m shooting a low key scene I will often use 500 EI so that I am assured of clean noise free shadows.
Just bought you a cup of coffee to say thanks for all this info. Will come from KP.
Can you please help me understand this?
On the FS7, you can shoot in Custom Mode using Gamma Slog 2 or 3 and the Matrix with a Pre-Select like Cinema. When you do that, the ISO is adjustable but has a base of 2,000. When you shoot in Cine EI, you can also shoot in Slog 2 or 3 with a locked ISO of 2,000, but you have a choice of color spaces. Is that the only difference between the modes? That is, with Cine EI, you get a choice of color space and VF Luts, but everything else is pretty much locked down, but in Custom Mode, you can still shoot with Slog 2 or 3 and the only thing locked down or limited is the Colorspace? Is that correct? I guess I am not really understanding the advantage of shooting in Cine EI over Custom. It seems Custom would pretty much give you much options, or is the choice of color space and VF monitoring worth it?
Thanks again.
If you are in custom mode and you change the gain away from 2000 ISO you will no longer have the full dynamic range which defeats the whole purpose of using log. In addition the color gamut is reduced and won’t match any LUT’s. Furthermore the Cine EI mode turns off things like noise reduction (which can lead to banding in log footage) and other things such as sharpening which are detrimental to log shooting.