A week or so ago I met another Sony FE user. He was using an A7r and I had my new A7s with me. We chatted for a while and he told me that he was trying the A7r at 15MP to see if that improved the noise levels.
A soundimageplus regular also posted around the same time his belief that DxO reduce the size of the files in their sensor tests, which would make sense since they always seem to ascribe somewhat 'magical' low noise / high ISO powers to 36MP sensor cameras which surprise me, since my experiences are somewhat different.
Thinking about those two things, I decided to see how my A7r compared to my A7s if I downsized the 36MP files to match the 12MP of the A7s. I also decided to see how the two cameras sensors performed at what might be described as 'normal' high ISO settings. i.e. 1600-12800. The A7s will of course go higher, but there are few occasions when I'd even contemplate that. But within the range I indicated, there are many situations when using that ISO setting would be useful. Below is what I got using the Sony FE 55mm F1.8 ZA Carl Zeiss Sonnar T* lens.
As well as the higher settings I gave ISO 100 a go first, and those downsized 36MP do make a difference. The A7s file is good but the A7r produces a sharper file. Moving upwards the A7s gradually shows a better, less noisy rendition as the ISO increases and by 12800 there is quite a marked difference.
I also ran two files through Adobe Raw at ISO 6400 to see what I could get out of the files in terms of dynamic range at high ISO's and surprisingly they looked very similar. So what's going on here?
Well, it's often been written that downsizing large MP files improves the noise levels and that seems to be the case here. It's not the whole answer as the samples above clearly show, but in a low light situation, if you have the opportunity to reduce the size of the files you are outputting, there IS an advantage to be be gained. Obviously with less pixels to work with, you can end up with a small file. Reducing a file from a 16MP sensor camera in the same proportions that I've done in these tests would produce just over a 5MP file. There are occasions when that might be enough, but many where it wouldn't be.
It's a (sort of) solution when using highly specified cameras that have large pixel counts, but no more than that. And again referring to the samples / tests above, the A7s is the better tool in a low light situation. So for me an interesting comparison and as ever the point of what I test is to add that knowledge to my memory banks for future reference. Plus with the fluctuating light levels in the UK this time of year that could be useful.
Just to say that regarding the A7s I am in the process of putting together a comparison between that camera and my Nikon Df, to see which is the better low light performer. There are already reviews and articles that suggest that the A7s has the advantage, but from what I've been seeing I'm not so sure, so I'm going to take some time to see how the two compare. However, more on that later.
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There is an interesting article on the BBC website HERE, which deals with many of the issues above.