Two astrophotographers sent me these messages. I am absolutely no Astrophotography expert but Sony may take note of their issues:
Nico (creator of the image on top): “As an occasional starscape photographer, I was impatient to see what i could get with the superior low light performance of my new Sony α7s Mk2. But unexpectedly, all my results were definitely worse than on my « theoretically inferior » previous Canon body. Searching the web, it appears that Sony has implemented the star eater, which was quite infamous among the small astrophotographers community on Sony α7s Mk1.
The star eater is a filtering aimed at removing any hot pixel on the picture. Simply put, it is a median filter on the raw signal. Such median filter erases any hot pixel, thus preventing the appearance of any chroma noise. But for people who want to photograph stars, that are 100% similar to a hot pixel on the raw signal, the star eater erases them too. This is especially bad when using a camera body like the Sony α7s with large pixels and sharp (and expensive) optics that deliver star images smaller than a pixel.
All my trials on the Sony α7s Mk2 show that the star eater is activated for any exposure larger or equal to 4s, and in any mode, any ISO. I have made a comparison by taking exposures of 3.2s and 4s to show the difference and stacked them. The effect is pretty disastrous with the vast majority of weak star totally erased on 4s images compared to 3.2s images. The same conclusion was also obtained by a deepsky astrophotographer on Sony α7R Mk2 (https://www.dpreview.com/forums/post/58706594).
This is really bad news for the whole community of starscape photographers, who typically use exposure duration from 5s to 30s and have access to very sharp optics. Therefore I wanted to share this in order to warn starscape photographers that if they use the Sony α7s Mk2, they will not be able to avoid the star eater, which will very strongly affect their images.
Sony has been aware of the star eater issue on Sony α7s Mk1 for years by the small community of disappointed deep sky astrophotographers (examples) who need bulb mode for getting exposure duration from 30s to 4 minutes. But Sony engineers have not fixed the issue, and they have even made the things infinitely worse on Mk2, because the star eater is activated for any exposure longer than 3.2s, and therefore affecting the much larger community of starscape photographers.”
Romain: “That’s not really a rumor, more of a “complaint” towards sony. But a huge and important one, and I think more people need to know the problem.
A lot of astrophotographers including myself made the evidence that sony is cheating on RAW files, adding what we call a “star-eater” algorithm to erase hot pixels.
It’s probably makes the image better for usual photography, but it essentially removes stars from astronomy pictures and induces a significant sensivity drop
When A7s was released, astronomers immediatly found out about that algorithm, but it was not that big of a problem because it only applied on shoots taken in BULB mode. Even in astronomy, 30s is enough for most purposes, so community was kinda fine.
Then, sony announced “uncompresed RAW” for its future line up of cameras, and we thought this stupid stuff was over. However, even in this mode, nothing changed and BULB mode was still unusable.
And recently, sony “patched” their algorithm with the most recent firmware ( 3.3 ) and extended the bad stuff to any exposure time above 3.2s on the A7R2. I have no data about the A7S2 and it may be concerned too, but luckily for us, our community is mainly using A7S ( since version 2 didn’t improve sensitivity ) and firmware didn’t come on that model.
So what, where is the real “RAW” file we all want ? Yeah, sony is providing “uncompressed cheated raw files” now. And it may be better looking at first for usual photography, but there may be some stuff we loose too, since no one really tested that. Furthermore, you can still apply that algorithm afterwards if you want.
Or something like an on/off switch in the menu would be perfect.
But I think many people would agree on the fact that sony should provide us “real” RAW files if we want it.
So I think this deserves to be known, and maybe then sony will react. Because we tried to contact them, and it didn’t do anything for now, probably because there is less than 10.000 astrophotographers…
Here is some links to prove what I say :