D3 sensor efficiency

Started Nov 18, 2007 | Discussions thread
Bill Janes Senior Member • Posts: 1,848
Re: D3 ISO Grossly Overrated?

The article by Christian Buil states, "The ISO sensitivity levels corresponds to an electronic gain extremely different between Canon and Nikon. Assuming that the quantum efficiency of sensors are equivalent (it is highly probable in first approximation), the displayed sensitivity of 6400 ISO for the Nikon D3 #1 corresponds to a sensitivity of 600 ISO for the Canon 40D, while a sensitivity displayed at 6400 ISO for the Nikon D3 #2, corresponds to a sensitivity of 2400 ISO for the Canon 40D. Analysis shows that the 'displayed' ISO announced by Nikon is very over evaluated relative to Canon competitor."

From the presented data, I find this puzzling. He compared the Canon 40D to the Nikon D3, both operating with a bit depth of 14. What he calls inverse gain for both cameras at ISO 400 was 0.78 electron/ADU for the Canon and 2.1 electrons/ADU for the Nikon. The Canon pixel pitch is 5.7 microns and that for the Nikon is 8.2. The ratio of the pixel areas is 1:2.22. If quantum efficiency, fill factor, etc are similar for the two cameras, the Nikon should collect 2.22 times more photoelectrons than the Canon at equivalent integration times, and this should affect the gain proportionally. The actual gain ratio is 1:2.7, roughly as expected.

Can anyone explain Christian's analysis?

Bill

p.s.

For Emil: Christian does take truncation of the data into account when calculating read noise.

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