Extreme low light video: a7s III Vs a7 IV

Entropy512 wrote:

RussellPhotoNerd wrote:

Howdy all,

I've been using a Sony a7s Mk1 for a year or so with a few decent E-Mount lenses which I use for both video and photo of the night sky an landscape. I am finding I am much more a video guy than a photo guy though, probably to a point of an 70/30 split.

I've been looking at the a7s III and more recently the a7 IV. The a7S line has always been considered amazing for low light, however I've been really impressed with the high ISO (25600+) video examples I've seen coming from the a7 IV. Given I shoot at 24p 1/25 with ISO between 25600 and 64000 in Slog-2, I would have thought the a7s III would have a fairly clear advantage here given it's 2nd native ISO is 12800 Vs the 3200 of the a7 IV. I'm guessing it is the significant over sampling of the a7 IV that is able to reduce the appearance of noise?

Anyway, just wondering if anyone could give me some advise on which of these two cameras would best suit my use case? For instance, would thermal noise performance at high ISO be better on the a7s III Vs the a7 IV? Honestly I'm really just a little bit baffled how comparable the two cameras look from the samples I've seen all the way up to ISO 51200.

PDR of both cameras for stills in raw is nearly identical (as is the case for almost anything newer than the A7R2) - https://www.photonstophotos.net/Charts/PDR.htm#Sony%20ILCE-7M4,Sony%20ILCE-7SM3

Note that all of those ISO ratings are in the camera's default picture profile. Take all of those and multiply by 8 for S-Log2.

HOWEVER:

Sony is kind of notorious for doing some sort of noise reduction for high-ISO video that you cannot turn off in the higher-resolution bodies. This may negatively impact the A7M4. Also, the A7M4, by virtue of having so many more pixels to read out, has much higher rolling shutter (26.8 ms for full sensor width vs. around 8.7 for the S3).

What is actually the case for A7M4 video hasn't really been determined for sure yet. But you can't make any assumptions because of the fact that the biggest difference in performance is going to be an artifact of the camera's processing pipeline and not inherently due to the resolution or sensor itself.

Thanks for the reply.

I'd not seen that PDR comparison before. Very interesting stuff.

Yeah, was prepared for the internal noise reduction drawback of the Sony ecosystem. I've actually watched a few more a7s III videos around night time usage (so super high ISO) and it seems that there is noticeable star eating above ISO80000. So from the point of view of using ISO for exposure, that would mean the a7s III would only have 2/3 of a stop usable advantage over the max ISO of 51600 on the a7 IV (without moving into extended ISO). Flip side, I have also watched Gerald Undone video on the a7 IV which indicates noise starts to become a real issue above ISO25600 which is more or less supported by Matt Johnson's review. Caleb Pike's video seems to show that noise performance is much closer at higher ISO's, so not sure where the differences are coming from here.

I'm getting the feeling that for my use case that these two cameras are going to perform very much the same. The real question I need to answer for myself is do I want the far superior video centric features of uncropped high frame rates and low rolling shutter of the a7s III for my non night time usage, or do I want the significant bump in resolution for a much sharper 4k24/30p image (albeit with inferior rolling shutter) and photography capabilities. The big bump in sensor resolution may also reduce the impact of the Sony star eater issue as they will cover more pixels which "should" enable to SOny internal NR pick-up that they are not noise.