Microfilm is 16 or 35mm film, usually unperforated, containing microreproductions (normally about one twenty-fifth of the original size) of images such as documents. Images are usually provided as black and white negatives, but positive images and colour are also used.
The standard length for roll film is 30.48 m (100 ft)for 35mm rolls, and 100 ft, 130 ft and 215 feet for 16mm rolls. One roll of 35 mm film may carry 600 images of large engineering drawings or 800 images of broadsheet newspaper pages. 16 mm film may carry 2,400 images of letter sized images as a single stream of micro images along the film set so that lines of text are parallel to the sides of the film or 10,000 small documents, perhaps cheques or betting slips, with both sides of the originals set side by side on the film.
Microphotography was first used in 1839 by John Benjamin Dancer, and microfilm saw military use in the Franco-Prussian War of 1870–71 as a means of allowing pigeons to carry dispatches in compressed form.
It was first used commercially in the 1920s. New York City banker George McCarthy was issued a patent in 1925 for his Checkograph machine, designed to make micrographic copies of cancelled cheques. In 1928, the Eastman Kodak Company bought McCarthy’s invention and began marketing cheque microfilming devices under its Recordak division.
Early microfilms (to the 1930s) were printed on nitrate film, which is explosive and flammable. From the late 1930s to the 1980s, microfilms were usually printed on a cellulose acetate base, which is prone to tears, vinegar syndrome, and redox blemishes. Preservation standard microfilms use the silver halide process, creating silver images in hard gelatin emulsion on a polyester base. With appropriate storage conditions, this film has a life expectancy of 500 years.
Unlike digital media, the format requires no software to decode the data stored thereon, but the images are usually too small to read with the naked eye and requires magnification to be read.