BTW, about viewing distance: since that is the official
subject, there is actually an optimum viewing distance provided
some assumptions are met. This is mainly that the taking lens is
orthographic (not sure this the right term. I means that a field
of squares, like graph paper, is reproduced as a field of
parallel lines on the image). The correct distance so that
parallel lines are seen as parallel is that the viewing distance
should be such that it is equal to the focal length of the lens
times the magnification of the image. So, a contact print should
be viewed from a distance equal to the focal length of the lens.
By memory its the focal length, not the distance of the lens from
the film since that can change if the lens is a telephoto or
reversed telephoto. For wide angle shots it means the eye must be
very close to the print. If not one sees the typical "distortion"
away from the center. In fact, its not distortion when the
perspective of the print is taken into account. The The edges and
corners are further from the eye than the center so appear
smaller. If a print fills the field of vision, a small print
close up or a very large one at some distance, the image will
appear orthoscopic, with no distortion away from the center. The
usuall distortion will make a spherical object appear egg shaped,
the distortion becoming greater as it is displaced more from the
center.
Except for wide angle pictures the distortion is not usually
noticeable. However, there is an optimal distance to view any
picture for the perceived perspective to duplicate that of the
original view.
Lenses that compress the outer parts of the image, such as
some types of extreme wide angle lenses do not produce
orthographic images to this trick doesn't work. The image is much
like that from photographing a reflective sphere.
On 8/25/2021 1:57 PM, `Richard Knoppow wrote:
I seem to remember a direct positive paper. I will look in my old Kodak literature to see if I can find it. I also remember seeing formulas for reversal processing of prints. Not sure why this was done except that B&W slides had some popularity and it would also make it possible to print from motion picture frames. At one time I could remember anything I read chapter and verse, not so good any more but my memory for that sort of thing is still pretty good.
On 8/25/2021 1:23 PM, MARK SAMPSON (msampson45) wrote:
Yes, SO-015 was a direct positive film. There was a similar product called “High Speed Duplicating Film”, I used them both at different times. VERY slow emulsions, both of them. And later I used a “rapid access” graphic-arts film called LPD7 that did the same thing. None of them required reversal processing, and must be long gone by now.
Mark S
Sent from my iPhone
On Aug 25, 2021, at 12:57 PM, Jeffrey Thorns <puresilver@xxxxxxxxx> wrote:
I don't remember a positive-to-positive b&w paper, but a think there were a few choices of 'inter-positive' films.
I think I remember taking original small format (4x5 and smaller) negatives and projecting them in an enlarger onto inter-positive film to create enlarged negatives for Van Dyke and Cyanotype printing. The film was quite expensive. The alternative was to use something like one of the (cheap) lith films (processed to produce continuous tone), make an enlarged film positive (from negative) in the enlarger, then contact printing onto the same type of film to arrive at an enlarged negative. You had to be *so* careful of dust and exposure and everything. You didn't want to go thru all that trouble and find some big nasty sitting on your 'giant' negative.
Definitely having flashbacks now. :)
<compose-unknown-contact.jpg>
ej@xxxxxxxxxxxxxxxxxxxxxxxxxx
August 25, 2021 at 12:48 PM
It was SO-015 and then ? 2205? It was processed in Dektol. Came in 8x10 sheet and possibly other sizes. It was a film. Print material? I don’t recall Kodak competing with Ilford on the direct print from slide material.
*From:* pure-silver-bounce@xxxxxxxxxxxxx <pure-silver-bounce@xxxxxxxxxxxxx> *On Behalf Of *Richard Lahrson
*Sent:* Wednesday, August 25, 2021 3:11 PM
*To:* pure-silver@xxxxxxxxxxxxx
*Subject:* [pure-silver] Re: print viewing distance
Didn't Kodak market a paper for direct
printing in b&w from slides? Does anyone
remember the name?
Laurence, as long as there's no hot water,
plastic is easy to work with.
On Wed, Aug 25, 2021 at 12:00 PM Laurence Cuffe <dmarc-noreply@xxxxxxxxxxxxx> wrote:
<compose-unknown-contact.jpg>
Richard Lahrson <mailto:gtripspud@xxxxxxxxx>
August 25, 2021 at 12:10 PM
Didn't Kodak market a paper for direct
printing in b&w from slides? Does anyone
remember the name?
Laurence, as long as there's no hot water,
plastic is easy to work with.
<compose-unknown-contact.jpg>
Laurence Cuffe (cuffe) <mailto:dmarc-noreply@xxxxxxxxxxxxx>
August 25, 2021 at 12:00 PM
I have drawn to a shuddering halt I’m my search for the perfect reversal print recipe. I was using a magic lantern slide, and a Stouffer test wedge as test images, contact printing onto the enlarger base board. The bronze u bend fitting below my darkroom sink, has sprung a hole. The darkroom was probably constructed forty years ago, so dissembling and replacing the plumbing, is not totally trivial. If I can’t repair the bronze fitting, I’ll probably go with plastic, as being more resistant to chemical mayhem.
Best regards
Laurence Cuffe
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<compose-unknown-contact.jpg>
Richard Lahrson <mailto:gtripspud@xxxxxxxxx>
August 25, 2021 at 10:22 AM
quite on the list lately!
Here's an amusing quote from Anchell:
"If the viewer stands only two or three inches away from
ANY print, it may appear fuzzy. However, only teachers, and students who are
trying to learn spotting techniques, should look that closely.
Anyone else is not appreciating the photograph."
