How Many Photons in a Photograph

Robin Harrison said:
Ok, that makes me feel a lot better, Brian. My 18% grey figure of 100,000 per pixel assumed:
a) all light that reached the sensor area actually reached a pixel, whereas even with the best microlens arrays, that won't be the case
b) a filter-less array

I'm guessing the RGB colour filters lose about two stops of light? And that the effective capture area is at best about 1/4 of the theoretical pixel pitch? In which case, we're talking about 100,000/16 = 6,250 photons per pixel, or 3.26 stops under the typical saturation levels you refer to. Not too far away!
Click to expand...

Well that's settled then ... just one thing, if they're actual particles hitting the sensor how do they carry any colour information?
 
Yep, mine too ... and for anyone thinking about posting that cat in the box thing, it really isn't dead and alive at the same time; it's actually either dead or alive, but we don't know which until we look in the box ...
 
Brian's well saturation number of around 60,000 seems to hold for pretty well all the high end sensors - CMOS or CCD. The you need to understand the efficiency of the sensor to work out the number of photons needed to saturate each pixel, and to make allowance for the loss of photons due to the Bayer matrix (which differes per colour).

Probably 60,000 * MP * 1.5 * x will get you there, for a digital sensor. Film would need more thinking about.

Mike

PS An interesting aside is that a 14 bit camera (i.e. one that outputs 14 bit raw files) with a ~60,000 well capacity and base iso of 100 (say a canon 1Ds3 or 5D2) counts partial photons above iso 400🙂 Or maybe not!
 
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