On Jan 17, 2004, at 4:55 PM, Tim Hughes wrote:
> An interesting aside somebody made at a
> talk I attended, was that although lensed chips increase sensitivity,
> the on chip lenses do
> not work well for very fast lenses, causing increased light dropoff,
> so the super fast
> lenses have an effective slower maximum aperture than you might expect
> from marked
> F-stop.
That is really interesting. I wonder if it is related to the diffusion
layer that is frequently used to limit moire. Maybe the diffusion also
flattens out the brightness a bit. I know that they are dealing with
reflection, too. There are instances when a lens at small aperture in
very bright conditions will have a light circle in the image that is
the result of light reflected from the sensor plane bouncing off the
back surface of the lens onto the sensor.
I also wonder whether the exposure circuitry takes the fast lens fall
off into account. Is it an even fall off or does it also get worse
toward the edge?
>
> The CMOS Foveon sensor should theoretically be much better in regards
> to
> using non-digital lenses as the wells are much shallower and the
> sensor area is at least 3
> imes larger per pixel, dramatically reducing the bottom of the well
> effects.
I have wondered about part of that. While the top sensor may be very
shallow and unlike a well, wouldn't the bottom one be in a well? Or is
the whole thing very shallow? I could see that at the edges of the
sensor the top pixel might be almost completely exposed while the
bottom one might get very little energy because of the angle. That
might make it difficult to get the color balance right at the edges.
Winsor
Long Beach, California
USA
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