Digital BW, The Print

Anton writes:

> Does this imply that if I am using B&W film (not C-41)
> where I have some control over development times etc,
> that I should calibrate the exposure/development time
> of the film optimally for the scanner's sensitivity range
> in order to maximize the tonal range? If this is the case,
> are there any guidelines for doing this?

If you know that you will only be scanning the image, never projecting it or
enlarging it, you can expose the film such that the areas of the image in
which you wish to preserve the most detail are exposed as neutral gray (and
thus in the center of the films sensitivity curve).  This maximizes detail
in those areas, and gives you more to play with on the resulting scan.
Sometimes this requires a slightly different exposure than normal visual
presentation would imply.

For example, if you photograph the inside of a coal bit on slide film, you
can expose for visual presentation or for scanning.  For visual
presentation, you just take an incident reading of the light hitting the
bin, and use that for exposure.  The result will be a slide that shows the
coal just as black as it appears in real life--but since the coal is very
black indeed, you'll lose a fair amount of detail in the coal because it
will be very near the exposure range limit of slide film.  For scanning,
then, you take a reflected reading and expose to make the coal nearly
neutral gray.  The coal will look weird in the finished slide, but when you
scan it, you'll get rich detail in the coal because all the detail now falls
in the middle of the slide's exposure range.  When you pick this image up in
Photoshop, you can adjust the curves to make the coal look truly black
again--but at least you'll have a wealth of detail to play with in the coal,
if you wish to accentuate it, whereas with visual exposure too much detail
would be lost.  The difference between the two is that the visual exposure
would give you a finished digital image that looks nice but lacks detail in
the coal, whereas a scanning exposure, coupled with the _correct_
manipulation in Photoshop, will give you a finished digital image that looks
nice _and_ shows rich detail in the coal, despite its blackness.

The only drawback is that you can never project slides that are exposed for
scanning in this way, because they will look incorrectly exposed.

All the same rules apply to negatives, but with negatives it's a bit easier,
since you never project those directly, anyway, and you have more exposure
range and a smaller density range to worry about.