At 01:16 PM 6/21/02 -0600, Daniel J. Mitchell wrote:
Well, doing the math; 21mm = 91 degrees field of view (convenient..).
So the center of the image is sqrt(2) ~= 1.4 times nearer than the corners.
Assume that those photos were taken with the center 30cm from the image,
then that puts the corners at 45cm away.
Depth-of-field isn't listed for the 21mm's, but the 24/2 at f4 (near
enough) with camera-to-subject distance of .3m gives an in-focus range of
29-31cm. In other words, it's not at all surprising that things 45cm away
(ie the corners) would be out of focus.
(even if the center of the map is, say, 50cm away, then the corners are at
75cm, but the in-focus range at f4 is only 47-54cm, so still plenty of room
for blur)
Hi Dan,
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.
Later,
Johnny
__________________________
Johnny Johnson
Lilburn, GA
mailto:jjohnso4@xxxxxxxxx
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