[filmscanners] RE: Scanning negs vs. slides

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

Anthony,

> Austin writes:
>
> > Well, yes they do eliminate it.  Because of
> > their exposure latitude and limited dynamic
> > range.  The exposure latitude clips the ends.
>
> And expands the midrange.

You conveniently snipped your original incorrect claim...only to add
this...which isn't relevant to your original claim being wrong.  It's an
annoyingly bad habit you have.  Here is what you said, and what I responded
to (and I quote):

"Slides compress image information; they do not
> eliminate it."

It's a fact, there IS information eliminated...no matter whether the
midrange is expanded or not.  What you said is wrong.

> So you are trading one type of information for
> another, but the total amount of image information on the slide
> is the same.

No, the amount of information on slide film is less.  Like I said, take a
step wedge, or a gradient and do the test for your self (correctly), and see
for your self.

> > That's not true.  Take a picture of a step
> > wedge and find out for your self.
>
> It cannot be otherwise, given the response curve of slide films, and the
> fact that film is a continuous-tone medium.  Since the curve is
> steeper for
> midtones than that of negative films, the difference between
> adjacent tones
> in terms of film density in that midtone range is much greater on slides
> than on negatives,

Well, it CAN be otherwise, and you believe it can't, because you don't
understand what dynamic range is.  Film is NOT continuous, though it gives,
to YOUR eyes, the appearance of, because the dynamic range of your eyes is
more limited than film is, for a given lighting condition.

> > Wrong.  The response curve has NOTHING to do
> > with representing the dynamic range/ability
> > to discern tones.
>
> Sure it does.

Well, no it doesn't.  Plain and simple.  Think about litho film, it has NO
midtones, and it has a very low dynamic range, but has a very high density
range.

> And the whole purpose of the steep curves of slide film, as I've
> indicated,
> is to better reproduce the dynamic range of a scene during
> projection.  The
> midtones of a slide can be projected with differences that much
> more closely
> approach those of the original scene;

That has nothing to do with dynamic range.  It's a property of what slides
ARE supposed to do, with no consideration for dynamic range at all.

> the drawback is that, since film
> density is limited in its range, highlights and shadows tend to
> lose detail.

Huh?  Slide film has a HIGHER density range.  It's exposure latitude that is
the limit (as well as density range, but that has to do with tonality, not
with density range)

> > Absolutely not true.  The exposure latitude for
> > positive film is far less than for negative film,
> > and given that, there is less scene information
> > recorded on slide film.
>
> Latitude is irrelevant.  The information-carrying capacity of the
> film is a
> function of its density range,

Again, you don't understand what dynamic range is.  Litho film, high density
range, low dynamic range...very low "information-carrying capacity".

Austin

----------------------------------------------------------------------------------------
Unsubscribe by mail to listserver@halftone.co.uk, with 'unsubscribe 
filmscanners'
or 'unsubscribe filmscanners_digest' (as appropriate) in the message title or 
body