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[filmscanners] Re: Scanning negs vs. slides



Austin writes:

> Ask Kodak.

I'm asking you, not Kodak.  You made the assertion.

> The reasons I gave, that you snipped ARE
> the right reasons.

Because you say so?

> Higher contrast means LESS tones, if they are
> both over the same density range.

Contrast and density range are inextricably linked.  Twice the contrast
means twice the density on film.  The number of intermediate tones that can
be resolved between two arbitrary densities is relatively constant across
negative and transparency films.  Thus, since slide films have more rapid
changes in density over a small range of exposure values, they record more
intermediate tones over this range than do negative films, which show a
slower change in density over a broader range of exposures.

> Density range is merely the overall range
> of density.

So density range = density range?  What does that tell me?

Let me try:  Density range is the difference or ratio between clear film and
the darkest color of the emulsion.  If clear film transmits 99% of light (it
never transmits 100%, of course) and the darkest part of the emulsion
transmits 0.5% of light, the density range is 198:1, which is the same as
7.6 f-stops, or 2.23 in the usual d-max notation.

> Dynamic range basically is how many discernable
> tones there are within that range.

Dynamic range has multiple definitions, but yours is not among them.  It can
refer to the entire range of magnitudes (of light intensity, etc.) that can
be usefully recorded, but it can also refer to the entire range of
magnitudes that can be accurately displayed or printed.

In the case of slide film, density varies rapidly with changing exposure;
most of the detail-recording capability of the film, then, is expended in
the recording of a narrow ranges of luminosities.  The density of negative
film varies far less with changing exposure (although still faster than the
magnitudes being recorded), and so the detail it can record is spread over a
wide range of luminosities.  Since both types of film offer roughly the same
granularity in recording (in this context meaning the same number of
discernable density levels from highest to lowest density), slides
necessarily provide more detail in the midtones, but less at the extremes of
light and shadow, as compared to negatives.

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