Monochrome sensor conversion... seeking advise

khunpapa wrote:

bclaff wrote:

Meuh wrote:

Any reason why you wouldn't buy a Sigma Merrill and use that in B/W selecting the blue channel only?

Photons of different energy (wavelengths) penetrate the silicon to a different depth.
Using only the blue (top) plane would not capture all the visible wavelength; only predominantly blue. You'd miss the green and red wavelengths that penetrate deeper.

You misunderstand this . Practically, that's Sigma's early statement's fault.

The top layer is only 1 uM thick (thin?). It absorbs all R G B photon. But because it's so thin & the P-N is doped to be higher band gap, the G & R (& some B) photon pass the top layer P-N junction almost without any interaction.

That's what's behind Sigma's new Quatro sensor. The top layer determines the resolution and color. The middle green and low red has 4 times larger P-N area to capture the remained photon, thus not only provides more accurate color information but also increases the QE considerably (1 stop, or 100%).

From one of the very early documents: Foveon Technology and the Changing Landscape of Digital Cameras we see absorption and penetration vary considerably versus depth (note the logarithmic scale).

What saves you is the wide color response of the top ("blue") plane.

However, the sensitivity as you head toward red drops quite a bit.
So yes, you can do it, but I suspect that effective Quantum Efficiency (QE), especially for red, is pretty low compare to a sensor that has had the Color Filter Array (CFA) removed.

Regards,