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Re: filmscanners: Scratched Negs & Home C-41 processing



Thanks for the details!  I'm no scientist or tech; I was a Wells Fargo VP in
a previous life.  I also have never printed color, so the matters you point
out would not have occurred to me.

Hart Corbett



----------
>From: Photoscientia <photoscientia@photoscientia.co.uk>
>To: filmscanners@halftone.co.uk
>Subject: Re: filmscanners: Scratched Negs & Home C-41 processing
>Date: Thu, Jan 25, 2001, 4:39 PM
>

> Hi Hart.
>
>> ......Collimated light, such a from a point source and then run through an
>> enlarger condenser increases the contrast ............
>
> I'm pretty sure that the contrast isn't increased with colour materials, for
the
> following reason:
>
> The contrast increase in B&W printing is due to the so-called Callier effect,
and
> is caused by the diffusion properties of the negative increasing with the
silver
> density of the image.
> Light through the clear film base is hardly diffused at all, and most of it
goes
> on to hit the enlarging lens, but in denser parts of the negative, some light
is
> scattered by the silver, misses the entry pupil of the lens, and so can't
> contribute to the printed (or scanned) image.
> That's how the contrast is increased, by the varying Callier co-efficient
> (co-efficient of light diffusion) of a B&W negative.
> However, the situation is different with colour materials, since they don't
> contain any silver.
> The dyes that make up colour images don't impart much turbidity to the
negative
> or slide, and the light diffusion is much more constant across the density
range.
> In any case, the mask of colour negative film means that the dye density is
> fairly heavy, even at it's most transparent.
> The Callier effect is therefore almost non-existent with colour materials, and
> the contrast varies very little with collimation of the light source.
>
> Of course, light scattering from a scratch will still occur with either a dye
or
> a silver image, and a collimated light source will definitely increase the
> visibility of surface defects.
>
>
>
>> but also increases the visibility
>> of any negative defects.  Collimated light essentially is where all the
>> light rays are parallel to each other.  Diffuse light (different than a
>> diffused image) was preferred, particularly from a so called "cold light"
>> source which is what I have had in my Beseler enlarger for many years.
>> [Something more learned from Ansel Adams, who printed with a cold light].
>> Even Adam's negs were not perfect, by any means! In later years, he had an
>> assistant whose job was to retouch his prints before they were matted and
>> framed.  He *never* exhibited an unretouched print.
>>
>> Hart Corbett
>>
>> ----------
>> >From: Roman Kielich <panromek@bigpond.com>
>> >To: filmscanners@halftone.co.uk
>> >Subject: RE: filmscanners: Scratched Negs & Home C-41 processing
>> >Date: Wed, Jan 24, 2001, 2:13 AM
>> >
>>
>> > At 07:18 23/01/2001 -0800, you wrote:
>> >
>> >>         In one case, I picked up some negatives which demonstrated a very
>> >>long scratch across several frames which didn't show up in the prints
>> >>(which I use as pseudo-proofs).  The significance of the scratch was
>> >>it should have showed in the prints, and my conclusion was the scratch
>> >>occurred during the printing process.  One method of avoiding this is
>> >>to use a service which puts the sticky laminate on the film after
>> >>processing, but before printing.  However, the laminate has it own
>> >>downside ... primarily being a hassle to remove before scanning.
>> >>
>> >>shAf  :o)
>> >
>> > if they accepted your argument, they deserve to be punished. Most printers
>> > use diffused light which "masks" fine scratches. The same neg printed with
>> > a point light source would look terrible. Saying that, I'd rather look for
>> > scratches which are not parallel to the edge. It is definite sign of a film
>> > abuse.
>> >
>> >
>> > "Don't worry about the world coming to an end today. It's already tomorrow
>> > in Australia".
>> >
>> >
>
> 




 




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