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

Started 2 months ago | Discussions thread
Pixel Pooper
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Re: a7S high ISO claim - - -over hyped or not ?
In reply to LSHorwitz1, 2 months ago

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.

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.

The 2 stop benefit is only at those ISO settings. At higher ISO the A7S will be more than 2 stops 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.

The max ISO setting is 6 stops higher, but that doesn't mean the performance is 6 stops better. I don't think Sony ever claimed that both cameras would perform the same at their max ISO settings.

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?

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.

To avoid the confusion which may arise from Sony's offering extended ISO beyond 102,400 to 409,000, I want to ask anyone who replies to please leave this extended claim out of the discussion. I do realize that further claims by Sony to extend the a7S to yet higher extended ISO of 409,000 makes the a7S appear to have yet additional sensitivity, but I would judge this to be no more than manually "push processing" the sensor further, no different from manually setting my NEX-7 to expose a couple more stops underexposed. I am trying to compare both bodies based entirely on their measured sensitivities for their normal claimed range of ISO.

With Sony sensors there is no difference between raising ISO and push processing apart from the lower DR at higher ISO. There is only one sensitivity, and every setting above base ISO is push processed.

Thanks for any insights here,

Larry

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