Inphotography,reversal film, orslide film, is a type ofphotographic film that produces apositive image on atransparent base.[1] Instead ofnegatives andprints, reversal film is processed to produce transparencies, ordiapositives (abbreviated as "diafilm" or "dia" in some languages likeGerman,Swedish,Romanian orHungarian). Reversal film is produced in various sizes, from35 mm toroll film to 8×10 inchsheet film.
A slide is a specially mounted individual transparency intended for projection onto a screen using aslide 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 asmotion picture film, mostly in the16 mm,Super 8 and8 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 successfulcolor photography reversal process was theLumièreAutochrome, introduced in 1907. It was anadditive method, using apanchromatic emulsion coated on a thin glass plate previously coated with a layer of dyedpotato starch grains.Autochrome plates were discontinued in the 1930s,[2] after the introduction of Lumière Filmcolor insheet film and Lumicolor inroll film sizes. Also using the additive principle and reversal processing were theAgfa color screen plates and films andDufaycolor film, all of which were discontinued by 1961.[3]
Leopold Godowsky, Jr. andLeopold Mannes, working with theEastman Kodak Company, developedKodachrome, the first commercially successful color film to use thesubtractive method. Kodachrome was introduced in 1935 as 16mmmotion picture film, and in 1936 as35mm film for still cameras.[4] Kodachrome films contain nocolor dye couplers; these are added during processing. The final development process published by Kodak asK-14 involves multiple re-exposure steps to sensitize the unsensitized grains.
In late 1936,Agfacolor Neu was launched,Agfa having overcome earlier difficulties with color sensitivity problems. This film had thedye couplers incorporated into the emulsion, making processing simpler than for Kodachrome.[3]
Earlycolor 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[5] 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 andadvertising photography, reportage, sports, stock and nature photography.Digital media gradually replaced transparency film.[6][page needed]
All color reversal film sold today is developed with theE-6 process. The non-substantiveKodachrome films, the last of which was discontinued in 2009, were processed with theK-14 process.[7]
Polaroid produced aninstant slide film calledPolachrome. It was packaged in cassettes like normal35mm film. A separate processing unit was used to develop it after exposure.
 | This sectionneeds additional citations forverification. Please helpimprove this article byadding citations to reliable sources in this section. Unsourced material may be challenged and removed. Find sources: "Reversal film" – news ·newspapers ·books ·scholar ·JSTOR(May 2009) (Learn how and when to remove this message) |
.jpeg)
Black-and-white transparencies can be made directly with some modernblack-and-white films, which normally yield negatives. The negative image is developed but not fixed. The negative image is removed by bleaching with a solution ofpotassium permanganate orpotassium dichromate in dilutesulfuric acid, which is removed bywashing and a clearing bath containingsodium metabisulfite orpotassium metabisulfite. The remaining silver halide salts are re-exposed to light, developed and fixed, and the film is washed and dried.[8]
Black-and-white transparencies were once popular for presentation of lecture materials using 3¼"×4" (3¼" square in the UK) glass-mounted slides. Such positive black-and-white projection is now rarely done,[citation needed] except in motion pictures. Even where black-and-white positives are currently used, the process to create them typically uses an internegative with standard processing instead of a chemical reversal process.
Black-and-white reversal films are less common than color reversal films.
.jpg)
Finished transparencies are most frequently displayed by projection. Some projectors use a sliding mechanism to manually pull the transparency out of the side of the machine, where it is replaced by the next image. Modern, advanced projectors typically use acarousel that holds a large number of slides; a mechanism automatically pulls a single slide from the carousel and places it in front of the lamp. Small externally lit or battery-powered magnifying viewers are available.
In traditional newsrooms and magazine offices slides were viewed using alightbox and aloupe, which allowed rapid side by side comparison of similar images.
Aslide copier is a simple optical device that can be fastened to thelens mount of a camera to enableslide duplicates to be made. Whilst these devices were formerly used to make duplicates on toslide film, they are often now used in conjunction with digitalcameras to digitize images from film-based transparencies. This method usually gives better resolution than using attachments for digital A4 flat-bedscanners.
The devices are typically about 30 cm long, and screw into an intermediate 't-mount' attached to the camera. The lens in the copier does not need to be complex, because the systems are usually stopped down to small f numbers (e.g. for the Makinon Zoom Unit,f/16 at 1:1 magnification, falling tof/22 at 3:1 magnification), and the object and image distances are similar, so that manyaberrations are minimized.
Films notably shot on reversal film include
