Originally posted by stevebrot Then you are aware that "shot noise" is only significant when photon flux is exceedingly low and essentially disappears when that is not the case. At least, that was how the discussion of Poisson distributions went when I took "Prob 'n Stat" back in the stone age.
It really depends on why and how it becomes significant, even when we are shooting at base iso it really is not that hard to find the tell tail signs of shot noise in a photo.
The biggest hurdle is that for the first 3 stops of the tonal range(zone10-8) in a scene is using 75% of the space a sensor can store as light information( signal).
take this photo
If you take a look at 100% you can see shot noise creeping in easily, on the right the image is take using the cameras meter set on middle grey and the right one stop larger exposure
https://photos.smugmug.com/Temp/Temp/i-cZF7J45/0/c819217b/O/_1710418%20crop.jpg
The reason why is how light information is captured, if we expose to the right and place objects found in a scene to appear as white close to clipping ( zone 10) as not to clip that signal is near saturation and we have captured a lot of information.
Now here lies the problem anything that falls in zone 9 only captures half the signal as zone 10. Here this still is not a big deal as our signal is still rather large and shot noise has very little influence.
Now we go to zone 8 it has only gather a signal that is 1/4 of the signal that zone
10
zone 7 gathers only 1/8 the signal
zone 6 gathers only 1/16 the signal that was captured in zone
10
Now we hit zone 5 middle grey has only captured 1/32 or 3% of the signal that was captured at zone
10 , now we start to see the tell tail signs of shot noise. 94% of the capacity of what the sensor can store is used up in the first 4 stops in tonal range of a scene. Naturally this is where we like to place most of the detail of our image is in zone 5 that only uses less than 3% of the saturation capacity of the sensor.
Dip down to zone 4 where we will place a lot of our darker tones and that is only made up of 1/64 of the light that the sensor can store( less than 1.5%) now shot noise is very easy to find.
Last edited by Ian Stuart Forsyth; 05-11-2018 at 10:38 PM.
Reason: correction in bold