I sometimes see filter densities expressed as 0.3 for 1 fstop, 0.45 for 1.5 fstops, 0.6 for 2 fstops...
Where do these numbers come from, and is there any way to make sense of them (other than
dividing by 0.3 to convert to f-stops :-)) ? For a moment last week-end, I couldn't remember how
to compensate for my 0.45 CF.