| Joined: | Wed Apr 11th, 2012 |
| Location: | Melbourne, Australia |
| Posts: | 525 |
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"Modern lenses resolve quite well, so let me explain this a bit more theoretically than practically. Imagine a lens that can only resolve lines about 6 microns in size (that would be one photosite wide in a 24mp FX sensor). What happens when you put that lens on a camera that resolves 4 microns in size (the photosite of a 24mp DX sensor)? Right, the lens isn't up to the capabilities of the capture system behind it and you'll be getting a little bit of edge blur as discrete lines spill over into part of an adjacent pixel. Moreover, let's assume that you're handholding and you move the camera 1 micron while shooting your image. In FX we've got a 17% pixel blur, in DX we've got a 25% pixel blur. (Remember, this is all theoretically arbitrary to help you understand the point I'm trying to make; in practice things are much more complicated.)
Technically, the FX camera is a more "relaxed" system than the DX camera when it comes to critical sharpness: FX can use lenses with a little less resolution than DX (all else equal), and you can handle the FX body a little more sloppily and get the same results you'd get in DX being more careful. While this may surprise you, this is not really different than the way it was with film. Medium format cameras could get by with lenses that were a little less resolution capable than 35mm cameras. That's not exactly the way people tended to use them, though: most medium format film users were trying to make bigger prints, so it was really the magnification issue that drove most of the 35mm/MF comparisons. As long as you didn't compromise the lens quality/handling in MF more than the extra magnification of 35mm, you were still better off, and if you didn't compromise those things at all, you were far better off."
Exactly what Eric has been saying about DX vs FX and technique.