a7S high ISO claim - - -over hyped or not ?

Started Jul 3, 2014 | Discussions thread
viking79 Forum Pro • Posts: 14,148
If you shoot RAW, I would look at DXO Low Light Sports score

LSHorwitz1 wrote:

As a long time satisfied NEX-7 owner contemplating the possible purchase of an a7S, I am trying to clarify just how much of an improvement in low light performance I might expect.

Using DxOMark measurements as a starting point, I see that my NEX-7 is rated at 1016 and that the a7S is measured at 3702.

What this is saying is based on RAW measurements, if you like the NEX 7 at ISO 1000, you should like the A7S at ISO 3700.

Understand that DXO resizes to a common output size. These are similar to the results you would get resizing your NEX 7 images to 12 MP before doing a pixel level comparison.

One might conclude that this measured less than a 4-fold increase in ISO should result in less than a 2 stop benefit, since each stop is a doubling / halving.

Yes, this is true. There is an approximate 2 stop flexibility advantage to the A7S. This is better than the 1 1/3 stop inherit in full frame vs APS-C, so this is saying the sensor in the A7S is in fact slightly better than the NEX 7 (but in line with A6000 or slightly better).

The comparison of the published specifications of two camera bodies as described by Sony however suggests a much larger gain, since one camera, the NEX-7, was specified as having a max sensitivity of 16,000 ISO, while the new a7S is described as having a max sensitivity of 102,400, over a six-fold improvement.

These numbers are for marketing purposes.

Is this claim by Sony over-stated, and thus the promised 6+ fold ISO gain increase claimed only really measureses to less than a 4 fold increase?

What claim by Sony? Those are not claims, just available ISO settings. The slightly less than 4 fold increase is what you would expect. This is a huge difference. It is like buying an f/1.4 lens instead of an f/2.8 lens (or maybe like f/1.4 and f/2.5).

I would be disappointed to go from my current NEX-7 and all my associated glass to the a7S at considerable expsnse, only to find that the DxO measured improvement of less than 2 stops was all that I gained.

That is a huge improvement. As an example, if you are shooting at your max tolerable ISO two stops means shooting at 1/250 instead of 1/60 (this means motion blur vs no motion blur for a walking person). In terms of lenses 1 stop is usually 2 times the price, so 2 stops would usually be a minimum of 4 times the price (but this is very approximate as lens price is influenced largely by market demands).

At the same time, if you don't need two stops flexibility, it is an extreme waste of money. I.e. if you are using a tripod for landscape work.

The A7S has a very specific market in mind, those that shoot events, etc, and need the high ISO capability, along with videographers who don't need more than 8 MP resolution (4K).

Nothing I say has anything to do with JPEG quality settings. I have no idea how they perform in JPEG. DXO mark should only be considered for RAW shooters (or those looking at sensor performance rather than JPEG engine performance).


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