In this answer I estimated that if a DSLR (digital SLR) camera with an aperture of 40 mm were pointed at a satellite in geostationary orbit with a visual brightness of about +11 magnitude, it would produce roughly 200 e- per second in the camera's silicon sensor.
I did a similar estimate here.
The estimate is only slightly better than order-of-magnitude. I assumed that the spectrum was reflected solar, and the average photon had about 2.5 eV of energy.
Is this about right? Is there any better way to do this starting with a given number meant to be "visual magnitude"?
I understand there are plenty of different definitions of magnitude that involve the specification of a specific band, (e.g. UBV) but when you are handed simply a visual magnitude, how can one estimate number of
photons electrons in silicon?
Yes, a precise calculation is quite sophisticated, but here I'm asking only for a good way to estimate. Let's call a silicon CCD's QE 0.8 and flat for example.