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filmscanners: Monochrome film speed/developer calibration for scanning?



Hi all,

I was reading the book Perfect Exposure today (Hicks & Schultz) and read the 
section on film testing. Struck me that for people like myself who have got 
rid of the wet darkroom, a method of calibrating a personal film speed and 
developer should be developed around scanning negs.

What it suggested for a simple test was that you shoot some frames with 
black velvet, an 18% grey card and a sheet of matt photographic paper (fixed 
and washed) bracketed around your meter reading. Then:

"the white paper should be detectable lighter than a piece of fogged and 
developed film, and the black velvet should be a good bit darker than the 
film base plus fog. If you have a densitometer, you can take actual 
readings. The black velvet should be at least 0.10 log units darker than 
fb+f and the white paper should have a density of around 1.1"

Now ideally I see a piece of software scan in a blank frame to get the fb+f 
value, and a totally overexposed frame to get a maximum density value. At 
that point a frame of the velvet/18%/paper can be scanned in and some small 
target areas of each tone identified.

The software can then scan in the rest of the frames and determine which one 
has the greatest contrast without flushing out either end. Another test 
could quantify the 'grainyness' of each patch by examining the distribution 
of values in the area, so different developers or under/overdevelopment 
could be studied

When the best patch has been identified the 18% grey section could be used 
for rudimentary gamma curve. Or even better, shoot one of those Kodak 20 
odd step monochrome grey scales in the image to get a more accurate version.

I imagine auto-exposure on the scanner could be a problem with this.

Any comments?

Regards
Ned


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