Instant film is a type of photographic film that was introduced by Polaroid Corporation to produce a visible image within minutes or seconds of the photograph's exposure. The film contains the chemicals needed for developing and fixing the photograph, and the camera exposes and initiates the developing process after a photo has been taken. In earlier Polaroid instant cameras the film is pulled through rollers, breaking open a pod containing a reagent that is spread between the exposed negative and receiving positive sheet. This film sandwich develops for some time after which the positive sheet is peeled away from the negative to reveal the developed photo. In 1972, Polaroid introduced integral film, which incorporated timing and receiving layers to automatically develop and fix the photo without any intervention from the photographer. Instant film has been available in sizes from 24 mm × 36 mm (0.94 in × 1.42 in) (similar to 135 film) up to 50.8 cm × 61 cm (20 in × 24 in) size, with the most popular film sizes for consumer snapshots being approximately 83 mm × 108 mm (3.3 in × 4.3 in) (the image itself is smaller as it is surrounded by a border). Early instant film was distributed on rolls, but later and current films are supplied in packs of 8 or 10 sheets, and single sheet films for use in large format cameras with a compatible back. Though the quality of integral instant film is not as high as conventional film, peel apart black and white film (and to a lesser extent color film) approached the quality of traditional film types. Instant film was used where it was undesirable to have to wait for a roll of conventional film to be finished and processed, e.g., documenting evidence in law enforcement, in health care and scientific applications, and producing photographs for passports and other identity documents, or simply for snapshots to be seen immediately. Some photographers use instant film for test shots, to see how a subject or setup looks before using conventional film for the final exposure. Instant film is also used by artists to achieve effects that are impossible to accomplish with traditional photography, by manipulating the emulsion during the developing process, or separating the image emulsion from the film base. Instant film is notable for having had a wider range of film speeds available than other negative films of the same era, having been produced in ISO 40 to ISO 20,000 (Polaroid 612). Current instant film formats typically have an ISO between 100 and 1000. Instant film has been supplanted for most purposes by digital photography, which allows the result to be viewed immediately on a display screen or printed with dye sublimation, inkjet, or laser home or professional printers. Two companies currently manufacture instant film for Polaroid cameras: Polaroid (previously The Impossible Project) for older Polaroid cameras (600, SX-70, and 8×10) and its I-Type cameras, and Supersense that manufacture pack film for Polaroid cameras under the One Instant brand.
How it works Instant positive film (which produces a print) uses diffusion transfer to move the dyes from the negative to the positive via a reagent. The process varies according to the film type.
Roll/pack film In 1947 Edwin H. Land introduced the Polaroid-Land process. The first instant films produced sepia tone photos. A negative sheet is exposed inside the camera, then lined up with a positive sheet and squeezed through a set of rollers which spread a reagent between the two layers, creating a developing film "sandwich". The negative develops quickly, after which some of the unexposed silver halide grains (and the latent image it contains) are solubilized by the reagent and transferred by diffusion from the negative to the positive. After a minute, depending on film type and ambient temperature, the negative is peeled away to reveal the picture which was transferred to the positive receiving sheet. True black and white films were released in 1950 after problems with chemistry stabilization were overcome. The reagent was contained in a pod, which would be pressed and eventually broken by the rollers that would then spread the reagent across the film. The reagent contained a solvent for silver halide such as sodium thiosulfate, for example. With that being said, photographers and enthusiasts still practice with this limited, special and discontinued film, with both older Polaroid stocks or Fujifilm FP-100C or FP-3000B varieties. Multiple companies made film backs that would adapt camera to use this film with a specific detachable back.
Subtractive color films Color film is much more complex due to multiple layers of emulsion and dye. The negative consists of three emulsion layers sensitive to the primary colors (red, green, and blue) each with a layer of developing dye beneath it of the complementary color (cyan, magenta, and yellow). Once light exposed the negative, the reagent is spread between the negative and positive and the developing dye layer migrates though diffusion to the positive surface where it forms the photo. Emulsion layers exposed to their respective color block the complementary dye below it, reproducing the original color. For example, a photo of a blue sky would expose the blue emulsion, blocking all the yellow dye beneath it and allowing the magenta and cyan dye layers to migrate to the positive to form blue.
… excerpt ends here. Continue reading the full article.
