Hello,

I've beeen searching quite a long time for the answer. In ISO/DIS 2240
there's is a color reversal speed defined as square rot between
Dfog+0,2 and tangent to shoulder or 2,0D exposure. Only the 2,0D point
gives right speed for low and high sensitivity slides. Everything is
good with this bonduary condition and with film speed equation:

ISO speed = 10/10^(logEs+LogEt/2)

Es - shoulder point (depends on norm)
Et - toe point (0.2+Dfog)

But this is only a synthetic speed based on HD curve. If you now take
a photograph of gray card then its density on film is somehow 1.25-1.4
- exactly how the repriocity of slide should be. From speed equation
density is lower - below 1,0D!

So can somone clairify this issue?
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                     Jack Zagaja - photographer, designer, programmer
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