Reversal film

From Wikipedia, the free encyclopedia

A single slide, showing a color transparency in a plastic frame

In photography, a reversal film is a still, positive image created on a transparent base using photochemical means. The terms slide and transparency are also used. Contrast with negative and print.

1 History
2 Characteristics
3 Black and white
4 See also

[edit] History

The earliest practical color photography was the Autochrome process. This was an additive 'screen-plate' method which produced a colour slide, but was fairly dim, and with the colour resolution limited by the fineness of the screen-plate.

The earliest practical method using a 'subtractive' method was the Kodachrome process, which produced much brighter color transparencies. Originally used mainly for news reportage, it gradually gained wider popularity. As a medium for serious amateur photographers, it gained popularity as an alternative to black and white print film starting in about 1945. Some amateurs were using Kodachrome for family snapshots as early as 1940 with many utilizing 35 mm roll film adaptors with common 4″×5″ "press cameras." At this time, color print 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.

Through to about 1995, color transparencies were the only photographic medium used for serious publishing, and were widely used in commercial and advertising photography, reportage, sports, stock, and nature photography. Digital media have since gradually replaced transparencies in many of 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 colour fidelity in digital media.

[edit] Characteristics

Slides are still generally preferred by professionals and many amateurs when working with traditional film. Slides are often sharper and have better colour reproduction. Generally, slides have a longer life span than colour prints. Kodachrome is well known for its archival qualities. Color does not fade in Kodachrome for a long time. Theoretically, they should last about 200 years; compare to 50-70 years for negative colour-film processes (e.g. Kodacolor or Agfacolor) and 20-30 years for colour prints. The Kodachrome process uses toxic and difficult-to-control chemicals in the development process and so remains in use in only a few locations worldwide.

Direct positive slide film is less forgiving of exposure errors than the negative - print - and development process chain. With negatives, the overall value may be sensed after processing and the exposure of the positive image controlled to compensate. The simplest point and shoot and disposable cameras do not even control exposure, a demonstration of the wide exposure latitude of the processes. It is also more 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.

A slide is a special type of transparency intended to be projected onto a screen using a slide projector. This allows the photograph to be viewed by a room-full of people at the same time. Slides were at one time an important medium for presentations, but LCD projectors which are now widely available have largely replaced traditional slide projectors for this purpose.

The most common form of modern slide is the 35mm slide, essentially a positive-image printing onto the standard 35mm film used in the movie industry, then placed inside a cardboard or plastic shell. 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.

Transparency film, in sizes ranging from 35mm roll film up to 8x10" sheet film, are produced by Kodak, Agfa, Konica, Scotch, and Fujifilm. Essentially all film sold today uses either 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.

Slide frames, 1940 (metal) to 1985 (plastic)

Slide viewer

Slide archive box

Slide frame 6x6 cm

[edit] Black and white

Black and white transparencies can be made directly with many types of black-and-white film using reversal-processing. It was 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. In the cinema black and white is used largely to reproduce a film noir appearance.

Black and white reversal films - which capture images in gray scales instead of colour as in color reversal films - are less common than color reversal films. Agfa manufactures the Agfa SCALA 200x Professional black and white reversal film for photography, which can only be developed with a special Agfa processing procedure by designated labs. As of April 2006, Main Photo & Imaging Service of California services much of the worldwide market for processing Scala. The dr5 lab in Denver Colorado also processes Scala.

Black and white reversal films are more commonly used in production of motion pictures, i.e. footage of video shot in black and white. The Kodak TRI-X Reversal Film 7266 is a black and white reversal film for movie making.

Kodak also currently produces a kit for reversal processing of TMAX film.