Originally posted by falconeye What you are saying here is that the back-LCD histogram isn't the 8Bit histogram of the RAW. This is interesting and I must confess I've never heard about. Do you have a link or search phrase to follow it up? Google or the forum search returned nothing specific for me.
What I am saying is that the histogram does not represent a 50% change in value for 1 F stop.
I just took 4 shots of my screne, with my *istD, and SMC-105mm F2.8. Each shot was at 1/125 but I stepped doen in 1/2 stop increments on the apature.
The back histogram on the first shot (correct exposure) was just to the left of middle. each successive shot moved further to the left, such that after 2 full stops (i.e. f5.6) I hade moved 1 division out of 4.
This is also how the histogram behaves in a photo editor.
As I explained previously, the distribution of an image and dynamic range is NOT done in a log finction,
The histogram is linea over the central part, in terms of histogram value vs f-stops.
each f-stop has an average value of 45 greyscale either in raw or with contrast set to neutral. it necomes non-linear at the high and low end, with 1 stop compressed into about a range of 17 and the next to a range of about 7. therefore overall, depending on contrast setting, you have a dynamic range of between 8 and 10 stops, with 4-6 very well behaved, an additional 1 on each side that is not too bad, and the last one whioch is really grainy and poor.