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. Reversal film is also a type of motion picture film that yields a positive image on the camera original without an intervening negative.
The earliest practical method using a 'subtractive' method was the Kodachrome process, the first commercially successful amateur color film, introduced in 1935. It produced much brighter color transparencies. It was initially offered in 16 mm format for motion pictures; 35 mm slides and 8 mm home movies followed in 1936. Originally used mainly for news reportage, it gradually gained wider popularity. Some amateurs were using Kodachrome for family snapshots as early as 1940 with many utilizing 35 mm roll film adapters 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.
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 color fidelity in digital media.
People still have slides at their homes, with the addition of digital media and digital photography, slides and transparencies can be digitized. The user needs a personal computer and an Image scanner capable of handling slides and transparencies. The scanner uses OCR or optical character recognition and TWAIN standards. The scanner must have an adapter for transparencies. Most scanners and also many AIO-or All In One machines should have an adapter for slides. After the slide is saved, it could be saved as a JPEG on a hard drive and could be transferred to a CD-ROM or a DVD-ROM. Most computers today have cd-writing capability. Most flatbed Image scanners range in prices of $49.00 for a basic model while for more professional use they range at $500 and up.
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, though inferior in resolution and color reproduction, 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 35 mm 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 and Fujifilm. Agfa, Konica, and 3M Scotch discontinued all their film production. Essentially all 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.
Black and white reversal films are less common than color reversal films. Agfa discontinued manufacturing their Agfa Scala 200x Professional black and white reversal film (along with their other B&W and color photo films), which can be developed either with their proprietary Scala processing procedure by Main Photo & Imaging Service of California, which processes much of the worldwide market for exposed Scala. The dr5 lab in Denver, Colorado also processes much Scala, along with many other conventional B&W negative films using their proprietary dr5 reversal-process, created by David Wood. The Foma company of the Czech Republic produces the only remaining dedicated black and white reversal film for 35mm stills, Fomapan R, which is also available in Standard 8mm, Double Super 8 and 16mm cine formats. Kodak & Foma currently produces a kit for reversal processing.
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.