>>I think FX files are generally of higher quality as they >need >>less enlarging to any size of output based on its larger >size >>of the sensor. > >I'm afraid that is not really the case. > >The relationship that matters in this context is between the >pixel dimensions of your image and the print size you want. A >12MP image will give you the same print resolution whether it >was captured on a DX or FX sensor. > >Where the FX sensor scores is that, for a given pixel count >each photosite will be larger, with benefits to things like >dynamic range, noise and tone/colour rendition. Put another >way, a 10.5MP DX camera using the same sensor technology and >firmware as a D600 (if such a device existed) would give >identical image quality.
Actually I have to agree with Berk, and I think he hits it right on the head. The pixel dimensions reasoning only holds up if pixels are of equal quality, and throwing in different sensor formats very much negates the "all things being equal" part of the equation. Ultimately you're magnifying your output less from an FX sensor, and that means, if the subject framing is the same, that you're magnifying other things less (camera shake, ISO noise, etc.)
The pixel size only limits your ability to resolve fine detail. The D800 proved it's not the large pixels of the D700 which gave such great dynamic range and high-ISO performance. In this case, Nikon triples the previous FX camera's resolution. Yes the pixels are now 1/3 the size, which means each is collecting fewer photons, which means lower signal, which means lower signal-to-noise ratio, but you can also downsample the images to 12MP, and now you have 3 independent measuring circuits simulating a larger photosite. Is it cleaner to measure 3 times and average that reading? It looks like the answer is yes, so forget about the idea that larger photosites are what made D700 better. The only challenge is, you've got to be able to analog-to-digital convert and move all that data in real-time. That wasn't reasonably doable in the D700's time, but it is today.
Of course the other side of the "all things are not equal" equation is the subject framing, which in cases where you are focal length limited, the question shifts back to pixel density. If you're shooting a distant subject with a 500mm lens and cropping from DX, then you've got quite an investment and a great deal of weight and bulk on your hands to frame that subject similarly with an FX camera, which is from where I believe the OP's question arises. Shoot the same subject with the same lens on an FX camera, and now you need to crop deeper to get the same framing. That negates the advantage of FX and means you need to look at the actual pixel-level performance to determine if there's any advantage.