Direct Positive duplicating film

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Trevor Davies
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Joined: Tue Jul 12, 2011 11:14 am Etc/GMT-1+01:00

Direct Positive duplicating film

Post by Trevor Davies » Fri Mar 22, 2013 2:28 pm Etc/GMT-1+01:00

This is a shot in the dark. I've been thinking about making LF B&W transparencies for a while and reading what's available on line. I just bought a box of out of date Kodak positive duplicating film (4x5) to play with.

I know it's very slow etc, but wonder if given the right conditions (long exposures of landscapes, still lives, etc, exposure/development balance) it might produce usable or interesting transparencies from a camera.

Does anyone have any experience or advice?


Emmanuel Bigler
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Re: Direct Positive duplicating film

Post by Emmanuel Bigler » Fri Mar 22, 2013 3:13 pm Etc/GMT-1+01:00

Hello from France

A few years ago, MACO in Germany marketed under the brand "Rollei Slide Direct" the same kind of film you are speaking about, and it was available in 5x4" as well as 120 rolls.
The film was said by MACO to be cut from master-rolls of Agfa Aerial direct-positive B&W duplicating film for B&W negatives. So it should work, no surprise.

Be prepared however, in addition to a tiny sensitivity in day light around 1 ISO (even smaller with tungsten light), that the film might be either non-chromatised (sensitive to blue only), or orthochromatic (sensitive to blue and green). Hence, you'll get the rendering of either pre-1900 non-chromatised silver halide films, or more recent orthochromatic films, i.e. blind to the red side of the visible spectrum and not very attractive for landscapes with clouds under a blue sky.

Otherwise, prior to this introduction of Rollei RSD film on the market, a French friend of mine had made some experiments by reversal processing of 5x4" and 10x8" B&W film, using the classical reversal process based on bleaching with potassium dichromate, 2nd exposure and 2nd development.

He wrote an article for our French MF/LF photo web site; the text is in French but you'll be able to understand most of its contents. Sometimes, for 10x8" film the gelatin would unfortunately go off the film support, my friend found it harder to process 5x4" and 8x10" than 120 rolls. ... blanc.html

Nevertheless he showed some nice 10x8" B&W slides. They are perfectly suited for projection with an overhead projector, those kinds of beasts being easy to find as a second-hand item, nobody wants them now ;)
I simply suggested my friend to make a slide holder frame in order to lift the slide by about 1 cm above the Fresnel lens, so that the rings are blurred in the image. Doing this you loose a bit of the illuminated field, but since overhead projectors are designed for an A4 size of documents, 10x8" being smaller you do not loosed anything in fact by lifting the slide enough to blur the Fresnel's rings.
For the 5x4" format however the overhead project will yield a small image ; in order to transform a standard overhead projector into a 5x4" slide projector you would need to change both the projection lens and the Fresnel lens. They are somewhat matched together, the Fresnel lens has a focal length approximately equal to the focal length of the projection lens; hence you would need a Fresnel lens of focal length twice smaller than the one in use in overhead projectors, and a projection lens with a focal length reduced by the same 0.5 factor; probably the proper focal length for projecting 5x4" [image size 94x120 mm ; diagonal f 150 mm] would be about 200 mm vs. 400 mm for a classical overhead projector covering 300x300 mm.
Fresnel lenses with a diameter equal to their focal length (i.e. a relative aperture of f/1) are common, in overhead projectors they are of this kind.
Many overhead projectors only use a single positive lens element as a projection lens, this is easy to find ; eventually the only question would be to find a proper Fresnel lens for projecting 5x4" more comfortably.

Trevor Davies
Posts: 20
Joined: Tue Jul 12, 2011 11:14 am Etc/GMT-1+01:00

Re: Direct Positive duplicating film

Post by Trevor Davies » Fri Mar 22, 2013 4:37 pm Etc/GMT-1+01:00

Many thanks, Emmanuel. Lots of useful information there! The film is old and cheap, so I'll do some experiments using your exposure suggestions and see where I get to. I wasn't planning projection at this point but that would opens up another new range of possibilities.
Best Wishes

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