Accurately comparing FF vs APS-C sensor performance? An open discussion.

Started Apr 8, 2013 | Discussions thread
VirtualMirage
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Re: Accurately comparing FF vs APS-C sensor performance? An open discussion.
In reply to Rab G, Apr 10, 2013

Rab G wrote:

You mention DXOmark what about camera iso settings compared with actual measured level have you looked at the A99 graph for that it looks bad really bad!!!

The A77 iso setting against measured setting seems to be much more accurate than the A99 so would that not make it difficult to compare shots supposed to be at the same iso ?

For example  snr 18% results

A99 measured  iso 439 manufacturers iso 800

A77 measured  iso 635 manufacturers iso 800

A99 measured iso 913 manufacturers  iso 1600

A77 measured iso 1302 manufacturers iso 1600

A99 measured iso 3762 manufacturers iso 6400

A77 measured iso 5412 manufacturers iso 6400

A99 is WELL out on all iso measurements.

Yep, I mentioned in my original post that I looked at that briefly as well but I felt it would get too convoluted to try to explain and understand correctly as well as everyone else understand it the same way as well.  The A77, on average, was around 1/4 - 1/3 of a stop off.  The A99, on average, was around 2/3 - 3/4 of a stop off.  But the A99 isn't the only guilty member of this party.  The D800e looks to be between 1/3 and 1/2 of a stop off and the D7100 is closer to a 1/2 stop off.  The closest one I have seen of the current cameras is the K5-IIs, which looked to be around 1/4 stop or less off.

I've created a full blown spreadsheet with both manufacturer's and measured ISO and their results via DXOMark for both print and screen.  I did this for the A99, NEX-7, A77, K5-IIs, D800e, and the D7100.  I even did my best to calculate the 1/3 stops in between each full stop since DXOMark doesn't show that to get a better estimate.

But what I wasn't completely sure of was what does it mean?

Are the cameras shooting at a slower shutter speed than they should?

Or

Are they shooting at the correct shutter speed for the manufacturer based ISO, which will underexpose the image, and then adding some positive exposure compensation through processing to have it match the proper exposure?

If it was the shutter speed varying, then it won't increase noise.  It would be quite the opposite.  But the cost is a longer shutter interval.

If it was the added exposure compensation in post, then that would increase noise but the shutter speed would be correct.

Since I wasn't sure of what it was exactly doing, I felt I couldn't accurately use it as examples if I didn't fully understand what was going on under the hood.

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Paul

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