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

Started Jul 3, 2014 | Discussions thread
(unknown member) Veteran Member • Posts: 9,509
Re: a7S high ISO claim - - -over hyped or not ?

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.

DXO is measuring low light performance, not high ISO.....some cameras get a score under 100 ISO.

The difference between the NEX-7 and A7S at higher ISOs will actually be greater.

They calculate the low light ISO score...

"The SNR indicates how much noise is present in an image compared to the actual information (signal). The higher the SNR value, the better the image looks, because details aren't drowned by noise. SNR strength is given in dB, which is a logarithmic scale: an increase of 6 dB corresponds to doubling the SNR, which equates to half the noise for the same signal.

An SNR value of 30dB means excellent image quality. Thus low-light ISO is the highest ISO setting for a camera that allows it to achieve an SNR of 30dB while keeping a good dynamic range of 9 EVs and a color depth of 18bits.

A difference in low-light ISO of 25% represents 1/3 EV and is only slightly noticeable.

As cameras improve, low-light ISO will continuously increase, making this scale open."


Dynamic range drops away on the NEX-7 more steeply.     Signal to noise seems to drop away similarly and colour depth drops away similarly after short slighter drop for the A7S.

Every review I have seen for the A7S says it is the low light king and most think it is pretty special.

Surprising to me since it seems to be more aimed as a video camera and it might get panned for that for rolling shutter and NOT having 15 stops of DR (even though its DR is better than anything like it).

I know I want one and may well get one at years end.

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.

I am not sure how much better it will be for you but I don't think there is anything better currently....maybe Canon will have something in a few months.


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