Advantages of Foveon sensor Locked

Started Jun 23, 2013 | Discussions thread
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OP Roland Karlsson Forum Pro • Posts: 27,409
Re: There is at least one absolute, and you refuse it.

xpatUSA wrote:

Bobn2 wrote:

Certainly, I was assuming visible light, between about 0.45 and 0.75 μm, where as you see from your graph the transmission is zero.

Zero??!! Fell right into the trap

May I recommend some light reading on absorption depth in silicon? It involves the probability of about 63% absorption vs depth for a given wavelength. In the graph above we see that, for 0.75um, 63% of photons are absorbed at a depth of about 10um in silicon leaving 37% free to proceed onward through the material. In other words, the transmissivity at 0.75um is 37% at 10um depth. Ergo, the transmission is not zero in spite of the claim made above.

Here's a 14MP Foveon sensor cross-section - not real thick as can be seen.

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SD9, SD10, EF-500, GH1.

Of course, its not zero ... then the Foveon would not work.

But, the absorption is very high for the visible range.

You say its 63% for extreme red at 10 um. As far as I remember, the Foveon sensor has a Q of around half that, as an average for the entire visible range. Is my memory right?

A quick glance at the transmission curve hints at green having 1/10 the absorption depth and blue 1/100.

So ... it feels like theoretically almost all blue and even green could be collected, and then 2/3 of the red. The latter depends on the scale in the image above. At what depth do you still detect photons?

So, a Q of approx 30% seems rather poor. Sounds like it, in theory, could be substantially improved.

Please tell me if my figures are seriously off.

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