Reversal film

In photography, reversal film is a type of photographic film that produces a positive image on a transparent base. The film is processed to produce transparencies or diapositives (abbreviated as 'diafilm' in many countries) instead of negatives and prints. Reversal film is produced in various sizes, from 35 mm roll film to 8×10 inch sheet film.Slide frames, 1940 (metal or card) to 1985 (plastic)Agfacolor slide dated 1939Agfacolor slide dated 1942Slide viewerSlide viewerSlide archive boxSlide frame 6×6 cmSlide frames 6×6 centimeters (2.4 in)A type 120 reversal film from the mid-1950s: the Italian Ferraniacolor In photography, reversal film is a type of photographic film that produces a positive image on a transparent base. The film is processed to produce transparencies or diapositives (abbreviated as 'diafilm' in many countries) instead of negatives and prints. Reversal film is produced in various sizes, from 35 mm roll film to 8×10 inch sheet film. A slide is a specially mounted individual transparency intended for projection onto a screen using a slide projector. This allows the photograph to be viewed by a large audience at once. The most common form is the 35 mm slide, with the image framed in a 2×2 inch cardboard or plastic mount. Some specialized labs produce photographic slides from digital camera images in formats such as JPEG, from computer-generated presentation graphics, and from a wide variety of physical source material such as fingerprints, microscopic sections, paper documents, astronomical images, etc. Reversal film is sometimes used as motion picture film, mostly in the 16 mm, Super 8 and 8 mm 'cine' formats, to yield a positive image on the camera original. This avoids the expense of using negative film, which requires additional film and processing to create a positive film print for projection. The earliest practical and commercially successful color photography reversal process was the Lumière Autochrome, introduced in 1907. This was an additive method, using a panchromatic emulsion coated on a thin glass plate previously coated with a layer of dyed potato starch grains. Autochrome plates were discontinued in the 1930s, after the introduction of Lumière Filmcolor in sheet film and Lumicolor in roll film sizes. Also using the additive principle and reversal processing were the Agfa color screen plates and films and Dufaycolor film, all of which were discontinued by 1961. Leopold Godowsky, Jr. and Leopold Mannes, working with the Eastman Kodak Company, developed Kodachrome, the first commercially successful color film to use the subtractive method. Kodachrome was introduced in 1935 as 16mm motion picture film, and in 1936 as 35mm film for still cameras. The Kodachrome films contained no color dye couplers; these were added during processing. In late 1936, Agfacolor Neu was launched, Agfa having overcome earlier difficulties with color sensitivity problems. This film had the dye couplers incorporated into the emulsion, making processing simpler than for Kodachrome. Early color negative film had many shortcomings, including the high cost of the film, processing and printing, the mediocre color quality, rapid fading and discoloration of highlights of some types of print that became noticeable after several years. Amateurs who owned projection equipment used reversal films extensively because the cost of projection equipment and slide film was offset by not having to pay for prints. Eventually, print quality improved and prices decreased, and, by the 1970s, color negative film and color prints had largely displaced slides as the primary method of amateur photography. Until about 1995, color transparency was preferred for publication because of the films' higher contrast and resolution, and was widely used in commercial and advertising photography, reportage, sports, stock and nature photography. Digital media gradually replaced transparency film. All color reversal film sold today is developed with the E-6 process. The non-substantive Kodachrome films, the last of which was discontinued in 2009, were processed with the K-14 process.