1 electron = 1 photon?

Started Apr 12, 2013 | Discussions thread
OP Jack Hogan Veteran Member • Posts: 6,517
Re: Photon rate vs Optical Power; Photon E vs bandgap

Marianne Oelund wrote:  Photons near 400nm do occasionally produce more than 1 electron in silicon, but the rate is low enough that it isn't a significant factor in the operation of our camera sensors.

Ok, thanks Marianne.  So if one were to try to calculate from an estimate of the sensor's electron output (calculated through shot noise SNR) the number of Exposure related photons reaching the area of the relative photosite, one could simply divide the number of electrons by a wavelength dependent conversion factor (what is sometimes referred to at various levels as QE).  Which brings us to the question of estimating this conversion factor.

1) I assume that for practical purposes one should use an average value across the sensor's spectrum for the conversion factor, a sort of effective QE, it being determined keeping in mind the spectral power distribution of the illuminating light and the wavelength dependent attenuating properties of the various filters/lenses/coatings above silicon, CFA and charge collection efficiency being two main contributors, right?

2) Intuitively I would use floating point math for this operation.  Is there a good reason why one should use integer math instead?

For instance if I do this for a D4 and D50 or so light off of DxO SNR curves, I get an effective QE of 15.9%, which for 7.01 e-/ADU at ISO 100 mean 44.11 photons/ADU.  electron Unity Gain is around ISO 700 and photon unity gain is around ISO 4400 - whatever the value of these gains is.


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