Sony A7s 5 stops brighter than NEX-5R??

Started Jul 8, 2014 | Questions
grprahl New Member • Posts: 5
Sony A7s 5 stops brighter than NEX-5R??

I do video work in the Outdoor industry, mainly a combination of video and timelapses which I always shoot as raw image sequences. I'm considering upgrading from the NEX-5R to the A7s because of the increased low light for video (in outdoor filming, low light is the norm rather than the exception). Let me know if I am understanding this right...

-According to DXOMark, the A7s has a usable ISO of 3702, whereas the NEX-5R has a usable rating of 910. This matches my previous experience that anything above ISO 800 looks a little too grainy. That's over 2 stops just from difference in sensitivity.

-According to Digicamdb, the A7s pixel area is 69.22 um^2 vs the 22.66um^2 of the NEX-5R. That's over a 3x difference in area. Does that also equate to a 3 stop increase in light gathering ability? Meaning that combined with the increased ISO sensitivity, I could expect roughly 5 stops of extra light gathering with the A7s and potentially use my f4 zoom lens at decent shutter speed when I would have had to switch to a f/1.4 prime in the past and slowed the shutter?

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uhligfd Senior Member • Posts: 2,842
Re: Sony A7s 5 stops brighter than NEX-5R??

I assume you know about equivalent exposures, and if you can shoot at ISO 3200 safely on the A7s where you only could use ISO 800 otherwise, you can film scenes that are 2 stops darker than before safely and nicely now.

Is that what you wanted to hear? Equivalent exposures. Period. Or ? ? ? ...

OP grprahl New Member • Posts: 5
Re: Sony A7s 5 stops brighter than NEX-5R??

if you can shoot at ISO 3200 safely on the A7s where you only could use ISO 800 otherwise, you can film scenes that are 2 stops darker than before safely and nicely now

That's part of it, yes. But I'm wondering if I can also film scenes that are an additional 3 stops darker due to the increased pixel area of the sensor.

exdeejjjaaaa
exdeejjjaaaa Veteran Member • Posts: 8,263
Re: Sony A7s 5 stops brighter than NEX-5R??

grprahl wrote: That's over a 3x difference in area. Does that also equate to a 3 stop increase in light gathering ability?

1 stop = double the area... 3 stops = 2^3 x area = 8 times

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blue_skies
blue_skies Forum Pro • Posts: 11,473
Re: Sony A7s 5 stops brighter than NEX-5R??

grprahl wrote:

I do video work in the Outdoor industry, mainly a combination of video and timelapses which I always shoot as raw image sequences. I'm considering upgrading from the NEX-5R to the A7s because of the increased low light for video (in outdoor filming, low light is the norm rather than the exception). Let me know if I am understanding this right...

-According to DXOMark, the A7s has a usable ISO of 3702, whereas the NEX-5R has a usable rating of 910. This matches my previous experience that anything above ISO 800 looks a little too grainy. That's over 2 stops just from difference in sensitivity.

Yes, and (almost) one stop more than the A7 has.

-According to Digicamdb, the A7s pixel area is 69.22 um^2 vs the 22.66um^2 of the NEX-5R. That's over a 3x difference in area. Does that also equate to a 3 stop increase in light gathering ability? Meaning that combined with the increased ISO sensitivity, I could expect roughly 5 stops of extra light gathering with the A7s and potentially use my f4 zoom lens at decent shutter speed when I would have had to switch to a f/1.4 prime in the past and slowed the shutter?

That is already accounted for in the DxOMark number.

DxO gives you the equivalent of 2 stops for 'low' or 'usuable' ISO.

When you go to high ISO, this factor increases for the A7s - check the graphs that DxO put up, as you see the dramatic improvement at higher ISO - and the A7s performs around 2 to 3 stops better than the A7! But we are talking ISO way past 6400.

At ISO 25,000, the A7s is more than 4 stops past the 5R... but even the A7s images will become grainy (however they do maintain the full-frame look).

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Cheers,
Henry

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