Quote Originally Posted by Daniel Browning


And it's especially untrue in the case of the 17-40. Even the $100 kit lens is sharper. This urban legend persists because of two common flaws in the method used to compare different format sizes: using different iris diameters and different magnifications. These factors must be equalized between sensor sizes to provide any sort of useful comparison baseline, and when that is done, it becomes clear that larger sensors are sharper (usually by even more than you would expect based on the lens price differential).
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I am really curious to hear more about this. You mention "larger sensors." I certainly agree that full frame sensors generally produce better, sharper images that resolve more detail (and I would have a FF body if money were no object). But I think you are saying something different above, although I am not sure I follow you. Please elaborate. I am by no means an expert or even amateur when it comes to optics, so I'd love to hear more.


Remember, though, that the only relevant comparison for me is the overall IQ of two different lenses on my 7d. You seem to be saying that the 18-55 kit lens would produce a better (or at least sharper) image on a 7d than the 17-40. Are you saying that would be true at identical focal lengths (ie, at say 24mm on each lens)? Or when you adjust focal lengths for the crop factor (ie at 17mm on the kit and 27mm on the 17-40)? In either case? My experience doesn't bear that out. Although the 18-55 is surprisingly good for a cheap lens, the color and contrast of the 17-40 far exceed the kit lens; and there's only so much sharpness the eye can manage anyway.


And are you saying that EF-S lenses will always be better on crop cameras than EF lens in the same/similar focal range?


Thanks!


Brian