Reversal film

In photography, a 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 in contrast with negative and print. Reversal film is produced in various sizes, from 35 mm, roll film to 8x10" 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, placed inside a cardboard or plastic shell for projection. Some specialized labs produce slides from digital images such as the jpg format, but also functions with computer presentation slides and slides from images such as fingerprints, microscopic sections, paper documents, telescopic images etc.

Reversal film is also used as motion picture film to yield a positive image on the camera original without an intervening negative.

Contents 1 History 1.1 Additive methods 1.2 Subtractive methods 2 Film types 2.1 Black and white 3 Uses 4 Displaying images 5 See also 6 References 7 External links

[edit] History

[edit] Additive methods

The earliest practical and commercially successful color photography process was the Lumière Autochrome process. This was an additive method, using a panchromatic emulsion coated upon a plate coated with a layer of dyed potato starch grains. Autochrome was discontinued in 1937 and replaced with Lumicolor in sheet film and Filmcolor in roll film sizes. Also using the additive principle were the Agfa screen-plate, Dufaycolor film and the Finlay plate, all of which were discontinued by 1961. ^[1]

[edit] Subtractive methods

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 in 16 mm motion picture film, and in 1936 for 35mm for stills cameras. ^[2] The Kodachrome films contained no color dye couplers; these were added during processing.

In 1937, Agafacolor 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. ^[1]

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Early color negative film had many shortcomings including high cost of film and processing and short print life. Amateurs who could afford slide film and projection equipment used it extensively until about 1970, when color print film began to displace it.

Until about 1995, color transparency was the only photographic medium accepted for serious publishing, and was widely used in commercial and advertising photography, reportage, sports, stock, and nature photography. Digital media have gradually replaced transparency film in these applications.

The use of slides for artists submitting to juried shows or applying for solo exhibitions, applying to art schools or for residencies (or the like), however, is still nearly universal for a number of reasons, among which is the actual or perceived lack of color fidelity in digital media.^{[citation needed]}

[edit] Film types

Essentially all color reversal film sold today is developed with the E-6 process or the K-14 process, with the overwhelming majority using the E-6 process.

Polaroid produced an instant slide film called Polachrome. It was packaged in cassettes like normal 35mm film. A separate processing unit was used to develop it after exposure.

[edit] Black and white

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Black and white transparencies can be made directly with some modern black-and-white film using reversal-processing. The process is used where transparencies are desired, rather than the negatives normally yielded by these films. First, the negative image is developed but the undeveloped silver halide salts are not removed by fixing. The negative image is removed by bleaching with a solution of potassium permanganate and sulfuric acid, which is removed by washing and a clearing bath containing sodium metabisulfite or potassium metabisulfite. The remaining silver halide salts are re-exposed to light, developed and fixed, and the film washed and dried.^[3]

Black and white transparencies were once popular for presentation of lecture materials using 4" by 5" glass mount slides. Such positive black and white projection is now rarely done, 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.

• Agfa-Gevaert discontinued its Agfa Scala 200x Professional black and white reversal film. This could be developed with their proprietary Scala process.

• The Foma company of the Czech Republic produces the only remaining dedicated black and white reversal film for 35 mm stills, Fomapan R 100, which is also available in movie film formats. ^[4]

• Kodak & Foma currently produce kits for reversal processing.

• dr5 chrome process.

Black and white reversal films are more commonly used in production of motion pictures.

• Kodak Tri-X Reversal Film 7266 and Kodak Plus-X Reversal Film 7265 are black and white reversal films used for movie making.^[5]

^[6]

[edit] Uses

Reversal films are the preferred film choice of professional photographers for images intended for reproduction in print media. This is because of the films' high contrast and high image resolution compared to negative (print) films.^[7]

[edit] Displaying images

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Finished transparencies are most frequently displayed by projection. Slides are cumbersome to display if only a few images are to be shown, although small battery powered direct viewers are available and suitable for use by one or two viewers.

Older projectors used a sliding mechanism to manually pull the transparency out of the side of the machine, where it could be replaced by the next image, and it is from this that we get the name "slide". Modern projectors typically use a carousel that holds a large number of slides, and viewed by a mechanism that automatically pulls a single slide out of the carousel and places it in front of the lamp.

Slide frames, 1940 (metal) to 1985 (plastic)	Slide viewer	Slide archive box	Slide frame 6x6 cm
Slide frames 6x6 cm

[edit] See also

• Slide copier
• Slideshow
• ViewMaster

[edit] References

[edit] External links

• Kodak TRI-X Reversal Film 7266
• Ilford B&W reversal processing description
• Ilford B&W reversal processing PDF manual
• Color Reversal Film Information and Comparison Chart