[filmscanners] RE: Scanning negs vs. slides

["Austin Franklin" <darkroom@ix.netcom.com>]

Anthony,

> Austin writes:
>
> > Slide film has a lower dynamic range (which loosely
> > translates into the number of tones the film
> > can capture...it's a little more involved than that,
> > but that's the basics of it) than negative film,
> > therefore negative film gives you more tonality.
>
> So why don't slide images posterize?  After all, if they can capture far
> fewer tones than negative film, I'd expect to see more abrupt transitions
> between different tones.

You really don't know the answer to that?  If slide film contains, say, 1000
tones, and neg film contains, say, 2000 tones, neither will posterize.

> I'd also like you to explain why slide film would have less dynamic range,
> given that it is essentially the same technology as negative film.

Ask Kodak.  Fact is, the dynamic range of slide film is less.

> > Slide film has a larger DENSITY range than negative
> > film.
>
> If it has a larger density range, but a lower dynamic range, I'd expect to
> see posterization.  Where is it?

See above.

> > Slides DO have more contrast for a number of reasons.
>
> The reason is that density varies more quickly with light exposure than on
> negative film.

I have no idea what you are trying to say there.  The reasons I gave, that
you snipped ARE the right reasons.  Are you talking about physical slide vs
physical negative, or are you talking about the resultant scan/print?
Higher contrast means LESS tones, if they are both over the same density
range.

> The density and dynamic ranges are the same,

No they are not.  Density range and dynamic range are NOT the same.  If you
don't understand that, then you don't understand what dynamic range is.

Density range = (dMax - dMin).

Dynamic range (dB) = 10log10((dMax - dMin)/noise)

Density range is merely the overall range of density.  Dynamic range
basically is how many discernable tones there are within that range.

Austin

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