Not exactly what you're after but I have a D700 and a D3200 (which is more or less the same as the D7100) and I much prefer the high ISO results from the D700.
I do know what you mean. And I'm sure in a direct ISO 6400 comparison the 610 would best the 7100 (to refer to OP's original post). However, the thing about full-frame is the depth of field is much shallower, so *for identical depth of field*, on full-frame one needs to stop down the lens. Leading to the ISO going up. Leading to more noise. So for a photo *identical in DOF and exposure*, I'm not sure there's as much in it between APS-C and full frame as one is commonly led to believe.
Incidentally, I have the same cameras as Nawty above. And although I would always use the D700 for low light work, for various reasons, interestingly enough the D3200 beats the D700 by one point on the DXO rankings, perhaps because of the extra pixels. So if you downsample the D3200 to 12MP, the race is a lot closer. Particularly if you expose for consistent DOF.
Prime example of why you shouldn't pay too much attention to DXO
All things being equal, ie similar generation sensor and processing engine, full frame will always beat APS-C in terms of noise and dynamic range, simply because it's bigger and captures more light/photons.
FF has more than twice the total sensor area of APS-C (difference is the crop factor squared, ie 1.5x1.5=2.25) so that's just over one stop better ISO performance. Dynamic range is slightly improved in the shadows by the same amount, as FF has twice as many photons to start with.
Depth of field is also reduced on FF compared to APS-C at same apertures, and the difference there is f/number x crop factor, ie f/4 x 1.5 = f/6, a smidge over one stop.
And sharpness is improved on FF because the bigger sensor needs less enlargement for a given size output/print. Therefore less resolution is required from the lens, therefore image contrast goes up and the picture looks sharper (regardless of pixel count, within reason).


I think you may have just sold me on a FF. Are you a salesperson by any chance. lol![]()
I think you may have just sold me on a FF. Are you a salesperson by any chance. lol![]()
I said 'tend' to be bigger and heavier. There's actually very little reason why FF cameras should be bigger than APS-C, but FF often comes in a higher spec and meatier camera body.
It's the lenses that are substantially bigger/heavier on FF, at equivalent focal lengths, eg
- Canon EF-S 55-250/4-5.6 is 108mm long and weighs 390g, price £210
- Canon 100-400/4.5-4.6 is 189mm long and weighs 1380g, price £1300