Advantages of Foveon sensor Locked

Started Jun 23, 2013 | Discussions thread
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OP Roland Karlsson Forum Pro • Posts: 27,871
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.

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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