I\'ll expand one point regarding the \"larger image circle\" issue. This supposed \"corner degradation\" on full frame is not quite the issue that some imagine it to be. There are are least two reasons for this.
1. For the same reason that the center of a full frame sensor image can have greater resolution than the center of a cropped sensor image, a given \"size\" distortions in the corners of a full frame image is smaller relative to overall image size in the larger format. (Think of expressing the \"size\" of the distortion is mm/frame width rather than mm.)
2. Because the larger format allows the photographer to stop down to smaller apertures at get overall diffraction-limited sharpness equivalent to that from larger apertures on the smaller format, shooting at the smaller apertures can, in many situations, compensate further for supposed corner image degradation.
I used to accept the notion that corners would be worse when a given lens was moved from crop to FF (especially with wide zooms) until I actually did this and found that in actual photographs this theory just doesn\'t play out that way. My 17-40 performs better in the corners stopped down to f/11 or f/16 on my FF body than it did at f/8 on a cropped sensor body.
Dan
brainiac wrote:
The simplest proof is theoretical: a 15Mp full frame camera can have much bigger sensels than a 15Mp crop camera. Larger sensels are better because they can gather more light, which means that they will have less noise and more latitude (dynamic range), and they will require less sharpness from a lens, but a larger image circle. Less noise and more latitude are indisputably good things for image quality.
Tolerance of poorer lenses is balanced by the downside that your lenses will be bigger, heavier, and more expensive to cover the larger image circle.
The depth of field differences are a double-edged sword: sometimes you want narrower d.o.f., and sometimes you don\'t. You can usually change your aperture one way or the other.
Jun 13, 2009 at 10:08 AM
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