Sony A7S II vs. Sony FS7 S-Log 3 Comparison Test

We shouldn’t be surprised that Sony A7S II is creating a lot of buzz these days. It’s definitely one of the most compelling, fully-fledged compact mirrorless cameras on the market that many cinematographers and filmmakers have been waiting for quite some time now. Yet, there is a certain concern about the apparent noise levels when using the new S-Log 3 gamma curve of the camera.

Some users have noted that when they view the ungraded S-Log 3 images it appears that the footage has more noise in the shadows than the one captured with the S-Log 2 profile. Well, it’s quite normal and there is a certain technical reasoning behind this. But before we plunge into details let’s first see a quick comparison test between the S-Log 3 gamma curve of the Sony A7S II and the Sony FS7.

The above test is another proof of the statement that not only the S-Log 3 gamma curve but all other S-Log modes in Sony cameras that provide this feature are different. In this particular case, we can easily see that the S-Log 3 on the Sony AS7 II is more washed out and flatten in a way compared to the one of the FS7. The colour bit depth is another aspect that also reflects final images.

In my opinion, the colour reproduction of the FS7 is a little bit more accurate and it’s quite normal given the fact that the camera records 10-bit video at 150MB/s, whereas the Sony A7S II is limited to 8-bit 4:2:0 recording only. Does this have to really bother you? Not at all. It simply means that when you apply a LUT to both clips the results will be slightly different, and you’ll have to put some extra effort to make both match.

Even with the limited 8-bit 4:2:0 colour subsampling on the Sony A7S II, the camera is completely capable of producing some lovely cinematic images, even in the most challenging low-light situations. Here is an example:

The video was shot in 4K at 25fps using S-Log 3 gamma curve. The maximum ISO used was 16,000. No noise reduction was applied. Despite the fact that the video was shot at night we can clearly see that it doesn’t have any noticeable noise issues in the final grade. However, according to Creative Grit who performed the test, the noise was evident in the S-Log 3 files. Once a LUT was applied in post, a little grading & 4K downscaled to a 1080p timeline, the noise is greatly reduced.

This proves Alister Chapman’s words that you won’t get any extra noise using S-Log 3 over S-Log 2 as S-Log 3 profile is generally easier to grade and work with in post production.

But how is that possible? Well, the simple answer would be that the signal to noise ratio of a camera is determined almost entirely by the sensor and it’s not changing between gamma curves. As Alister points out even though the shadow and low-key parts of the scene are shown and recorded at a brighter level, when shooting with S-Log 3 (in comparison to S-Log 2) the noise level appears to be a bit higher, however the ratio between wanted picture information and unwanted noise is exactly the same in both S-Log modes.

Furthermore, S-Log 3 has a nearly straight line curve. This means that in post production it’s easier to grade this footage as the adjustments applied will have a similar effect to all parts of the image. Furthermore, S-Log 3 gamma curve is also very close to Cineon and to Arri Log C and in many cases LUT and grades designed for these gammas will also work pretty well with S-Log 3 profile.

Overall, noise levels shouldn’t be your main concern when using the S-Log 3 mode of the A7S II.  It’s more important to get the optimal exposure and be a little bit more careful with your highlights as the S-Log 3 is slightly less forgiving of overexposure than S-Log 2. With that mind, I simply don’t see any objective reason not to use S-Log 3 profile on a day-to-day basis over S-Log 2.

Guys, what are your impressions on filming with S-Log 3 either on the A7S II or FS7? Share your opinion in the comments below.

[via: Cinescopophilia, source: XDCAM-USER]

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  1. Guillaume Juin October 26, 2015
  2. Duncan Dimanche April 1, 2016

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