Sigma SD1 - Holy c r a p

Started Sep 21, 2010 | Discussions thread
Victor Engel
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Re: Different diffraction
In reply to noirdesir, Sep 22, 2010

noirdesir wrote:

Victor Engel wrote:

But why would the (red) photodiode of a 15 MP Foveon sensor be any smaller then the (red) photodiode of a 15 MP Bayer sensor (ie, why would this more of concern for Foveon than Bayer)?

They would be the same size, but the Foveon one needs to be bigger. When the light falls on the top layer (blue layer) some of the light diffracts around the edges of the photodiode. This happens again in the green layer. By the time it reaches the red layer, a significant portion has spread to neighboring pixels.

The same is true on a Bayer sensor. However, the Bayer sensor also gets more red signal from the upper portions of the photodiode that would correspond to the blue and green layers on the Foveon. So more of the red signal that's actually used for red discrimination is less diffused on the Bayer sensor than on the Foveon sensor.

This is really just theoretical from my knowledge of how the sensors work. I don't have data to back this up.
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