From: William Sommerwerck <williams@xxxxxxxxxx>
<snip>
A word about lens compatibility. The cells in a CCD sensor sit slightly
below
the conductive paths that surround them. This means that, the more-acute
the
angle of light striking the sensor, the greater the shadowing effect of the
paths, further exaggerating the normal edge falloff that occurs with
wide-angle
lenses.
<snip>
This is part of the equation, the other (probably more significant) part of
the equation is micolenses. These are small "bubble" lenses over each
pixel, that focus incident light onto the active area of the pixel, which
generally is a small fraction (>25%) of the total pixel area. The angle of
acceptance of these lenses is generally <10?. Since silver-based films had
no anlge of acceptance requirements, no care was taken to control this
parameter.
<snip>
So I did some research. In every reference I checked, a lens's focal length
is
_defined_ as the distance from the exit node to the film plane. In other
words,
you can't change the position of the node without simultaneously changing
the
lens's focal length. QED -- Olympus's claim is not kosher.
<snip>
As others has mentioned. There are optical design techniques to get around
this.
<snip>
Regardless, the problem of edge falloff -- whatever its cause -- is easily
solved in software. It's a trivial matter to "map" the falloff for each
lens,
then process the image to remove the falloff. This could be done in the
camera
or with an image-editing program.
<snip>
This of course pre-supposes that this is enough energy with a sufficient
signal-to-nosie ratio to perform processing on, which may not be the case
with extreme angle-of-incidence.
If my understanding is incorrect, or otherwise flawed, corrections are
welcomed!
Cheers,
Kerry Frohling
Fullerton, California USA
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