> I don't believe that lenses are designed so that the points of critical
> focus form a semi circle in front of the lens as you describe. They're
all
> designed to focus on a flat field but some like the macros, are just
better
> at it than others. For example, if you are taking a picture of a group of
> people you don't need to arrange them in a semicircle in front of the
> camera - you put then in a straight line.
Oh, right; I wasn't sure what was going on with the optics here, I'll
admit. Still, expecting any lens to be able to correct for a 50 0reater
distance at the corners than the middle, um, actually does seem reasonable,
I guess, that's what they pay those lens designers for, after all..
On the other hand, this would mean that if you focussed on something at the
center of the image and then shifted the point of view of the lens by moving
sideways (rather than by rotating the camera) so that it was now in the
corner (without refocusing), it'd be blurred, because the lens would be
correcting the wrong way at that point. I guess you have to pick which way
around you want it to go and deal with the consequences.
-- dan
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