At 9:37 AM -0500 10/29/02, w shumaker wrote:
At 06:56 PM 10/27/2002, Winsor wrote:
<snip>
That is interesting and I am sure you are right, but I am not
entirely convinced. If you put a recessed sensor in a chip and
then create one 3 times as wide and 3 times as deep I am not sure
that you have gained anything. Since the bigger sensor elements
are probably thicker it is probably more than 3 times as deep.
<snip>
I think there are several reason for better potential performance of
the Foveon chip. The Foveon chip uses the fact that different
wavelengths of light are absorbed in doped silicon at different depths.
Shorter wavelengths are absorbed near the surface (blue light) while
longer wavelengths absorbed deeper (red light). The ion implantation is
adjusted to the different color depths to create junction isolation in
the silicon to electrically capture the different wavelengths. There
are no filters stacked on top of the silicon. The doped silicon itself
is the color separator. The deepest junction is only 2 microns deep for
red light. The junction depth of a CCD charge bucket is probably deeper
(10um? more) plus you have the RGB filter coating thickness. Hence the
steeper the angle of the light before it is absorbed and converted to
photos is going to be worse for CCD type images. It is filtered before
it is absorbed in the silicon. Combine with the RGB pattern and you get
the effect of chromatic aberration.
If the deepest junction in the foveon chip is only 2 microns down, then for
any reasonable number of pixels in full-frame you're talking about trays
rather than buckets.A 10 micron sensor pitch (about 10x the area of current
CCD's) would give you about 8.5 megapixels, probably equivalent to at
12 megapixels of interpolated CCD.
hmmm.
paul
--
Paul Wallich pw@xxxxxxxxx
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