One thing missing from his discussion is the angular dependency of the filters. They are most likely dielectric, and dielectric filters are dependent on the angle of incidence of the light. I light falls from an angle different from perpendicular the wrong colour will be filtered out.
Of course it is not necessary to have strictly parallel light rays, he is right in that this would not make any images, but you do need "more parallel" light rays than with film. Therefore some lenses, especially wide angles, are not suitable for digital cameras. Micro lenses does help a bit, but not enough.
DagT
P� l�rdag, 9. august 2003, kl. 04:50, skrev Mark Roberts:
Here's a post from one-time PDML member Bill Peifer on this subject. (He's PhD who works in optics in Rochester):
All this talk about "analog" vs. "digital" lenses has got me wondering a
bit. I'm curious where this whole idea of CCD sensors requiring (or
preferring) perpendicular rays originated. I'm pretty convinced that it
must have originated because somewhere along the line, something got
taken
out of context, and a fundamentally incorrect idea grew from there.
From
the standpoint of the underlying physics, Tom is absolutely right -- the
purpose of a lens is to bring an image to critical focus at the focal
plane,
and the nature of the sensor (film, CCD, CMOS, or other) isn't
particularly
relevant. After all, if all the light rays strike the sensor
perpendicularly, then they are necessarily parallel and thus cannot form
an
image at the focal plane!
I suspect that this perpendicular-ray story -- dare I say "legend"? --
may
have originated from a misinterpretation of the characteristic behavior
of
CCD sensors. We all know that in single-chip color CCD sensors, some of
the
pixels are sensitive to red, others to green, and still others to blue.
For
the case of color cameras with single CCD sensors, color sensitivity is
imparted to a particular pixel by incorporating a microscopic optic -- a
lenslet and filter -- in front of that pixel, which I believe is
accomplished as part of the manufacturing process for the sensor chip.
+++++
