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Re: [OM] Kodak's 14MP SLR

Subject: Re: [OM] Kodak's 14MP SLR
From: Winsor Crosby <wincros@xxxxxxxxxxxxx>
Date: Sun, 27 Oct 2002 15:56:30 -0800

Winsor, It should be very approximately 3 time better for Foveon, because the normal Beyer pattern reduces the area per colored pixel by approximately 3, while the Foveon chip does not. (stacked vertically rather than horitontally) This means if the depth of the pixel diffusion layers in the case of Foveon, are the same as the filter layer of a conventional chip the shading effect is greatly reduced. The lateral angle of acceptance would be much greater allowing wider angle lenses. It could be even better than this, since the sensor pixel area is reduced still further by metalization and interconnect between pixels on th chip surface. This added overhead is probably greater for smaller pixels putting them even deeper realtive to Foveon. One might guess the diffusions in Foveon's chip are also thinner than an on-chip filter, improving things further. In fact for the first layer there should be little to no lat! eral effect. This means the sensitivity drop off with lateral light rays is probably different for the three colors leading to yet another variation in color sensitivity with extreme wide angle lenses! This may be a negative for Foveon but given the chip should work with much wider angle lenses to start with it is probably still much better.

Tim Hughes

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.

I looked at the Foveon site again and I really do not understand it. It seems to me that one would have to still filter the elements, but if you did the bottom two elements would get no light. They say they are using the silicon substrate essentially as a filter since different colors penetrate to different depths. Perhaps it is digital math. The top layer measures all the light. The second layer measures the red and the green, and the bottom layer measures just the red. Some subtraction and you get the values. So I guess the question is whether three transparent Foveon sensors and two silicon layers of the required filtering thickness is thicker than a single mosaic sensor and filter.
Winsor Crosby
Long Beach, California

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