The duper is a hinged contact printing frame which provides for the simultaneous exposure of film from three original slide by using it in conjunction with either an overhead light source (an enlarger) or an underneath one. In essence, the Duper, light source, and operator altogether become a lens-less peg-registered copy camera. The working parts of the Duper include a "contact frame" and a "pressure plate." The contact frame is a flat plastic bed with three rectangular light openings arranged side-by-side, and set parallel against a row of registration pegs. Before attempting an exposure, the operator places three film originals onto the contact frame and its pegs. Then, with white light turned-off in the darkroom, unexposed film stock is placed, emulsion-side-down, onto the contact frame and originals. After closing the pressure plate over the sandwiched film, the Duper's light source is then illuminated for a specified period, to stream through the originals, exposing the raw stock. After all exposures are complete, the film is developed revealing copies (high contrast in the case of LPD4) which can be instantly mounted in-register with the originals in pin-registered slide mounts. When the next three slide originals are mounted on the Duper and the lights turned off, the operator uses the Duper's "cartridge track" to measure out the required length of film for the next exposure.
As stated earlier, the Duper can be used either under an enlarger or over a dedicated light source. In the former case, the contact frame and pressure plate (raw film and slide originals sandwiched between) are flipped upside down for the exposure. I prefer the underside light source method of contact printing. This requires the simple construction of a non-diffusion light box onto which the Duper is then mounted, but it makes the process faster and more convenient than using an enlarger. This project takes only a few hours to complete.