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# Quantum efficiencies for Canon DSLRS

Started Feb 12, 2010 | Discussions thread
Re: Quantum efficiencies for Canon DSLRS

The QE of the 30D is the same as for 40D or 20D, thus around 30%.
I will add the result for Canon G11 the next days.

Please not, that the QE is just an important sensor characteristics and does normally not correlate to IQ. On the other hand, better QE helps to avoid noise in low light situations.

Here are work flow to calculate the QE from the DXO-data:

QE = Fullwell [e- per pixelarea] / photon density P [Ph per pixelarea]

1. Calcualtion of the photon density P from the ISO sensitivity
First the measured ISO has to be transformed into expose H [lux s]:
H = 78 / ISO

Using the definition of illuminance I get 1 lux = 4.1E9 Photons/mm² s for 555nm light.
Thus, photon density is P = 4.1E9 x 78 / 1E6 = 320112
ISO [Ph/µm²]

2. Calcualtion of the Full Well Capacity

I evaluate the "Full SNR" data using the noise equation used by DXO-lab: http://www.dxomark.com/index.php/eng/Technologies/Noise-characterization/Summary

This curve fitting was done with excel. With this I was able to fit the read nosie, the full well capacity and the PRNU (pixel response non uniformity). I did this fit for 400, 800 and 1600 ASA.

3. Finally, I calculated the ratio QE = FW / P which is the quantum efficiency of the pixel.

This QE is for the greeen channel, since this channel saturates as first. I am working to get also the QEs for the red and blue channel using the "Relative sensitivities" data from DXO.

So, this was a lot of theory. The reason why I did this was mainly to know which DSLR is the best for astrophotography. For that use QE is very important!!

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