[tig] printer points exposure and ire:

Dominic Case cased
Fri Sep 3 02:02:53 BST 2004


The correlation between lab printer points and exposure stops is something I
can help on.

Executive summary for cinematographers: 1 stop is 7 printer points. But it's
not that simple. Read on . . 

One printer point alters the printing exposure by 0.025logE. 
As exposure is a logarithmic function, 0.30logE (or double the exposure)is
one stop.

So IN PRINTING TERMS, a printer point alters the exposure to the print stock
by 1/12th of a stop.

BUT, in terms of the negative, it's a little more subtle. The gamma (a
photographic term only partially related to that knob on your telecine) of
the negative emulsion comes into play. If I change the exposure  in the
camera by one stop (0.30ogE), then the density of mid-tones on the negative
will be changed by 0.30 times the gamma of the negative. That is about 0.55
- 0.57 for most stocks. Resultant density change is 0.30 x 0.55, or about
0.17logE.  

To compensate for a negative that is 0.17 lighter or heavier in density, you
need that much less (or more) light in the printer.  0.17/0.025 is about 7
printer points.

_________________________________
Dominic Case
Atlab Australia
________________________________



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