Microforms are scaled-down reproductions of documents, typically either films or paper, made for the purposes of transmission, storage, reading, and printing. Microform images are commonly reduced to about one twenty-fifth of the original document size. For special purposes, greater optical reductions may be used.
Microphotography was first suggested as a document preservation method in 1851 by James Glaisher, an astronomer, and in 1853 by John Herschel. Both men attended the 1851 Great Exhibition in London, where the exhibit on photography greatly influenced Glaisher. He called it "the most remarkable discovery of modern times", and argued in his official report for using microphotography to preserve documents.
In 1906, Paul Otlet and Robert Goldschmidt proposed the livre microphotographique as a way to alleviate the cost and space limitations imposed by the codex format. Otletís overarching goal was to create a World Center Library of Juridical, Social and Cultural Documentation, and he saw microfiche as a way to offer a stable and durable format that was inexpensive, easy to use, easy to reproduce, and extremely compact. In 1925, the team spoke of a massive library where each volume existed as master negatives and positives, and where items were printed on demand for interested patrons.
For example, when airlines demand archival engineering drawings to support purchased equipment (in case the vendor goes out of business, for example), they normally specify punch-card-mounted microfilm with an industry-standard indexing system punched into the card. This permits automated reproduction, as well as permitting mechanical card-sorting equipment to sort and select microfilm drawings.
Libraries began using microfilm in the mid-20th century as a preservation strategy for deteriorating newspaper collections. Books and newspapers that were deemed in danger of decay could be preserved on film and thus access and use could be increased. Microfilming was also a space-saving measure. In his 1945 book, The Scholar and the Future of the Research Library, Fremont Rider calculated that research libraries were doubling in space every sixteen years. His suggested solution was microfilming, specifically with his invention, the microcard. Once items were put onto film, they could be removed from circulation and additional shelf space would be made available for rapidly expanding collections. The microcard was superseded by microfiche. By the 1960s, microfilming had become standard policy.
A microfilm printer contains a xerographic copying process, like a photocopier. The image to be printed is projected with synchronised movement on to the drum. These devices offer either small image preview for the operator or full size image preview, when it is called a reader printer. Microform printers can accept positive or negative films and positive or negative images on paper. New machines allow the user to scan a microform image and save it as a digital file: see the section below on digital conversion.
The most commonly used format is a portrait image of about 10 x 14 mm. Office-size papers or magazine pages require a reduction of 24 or 25 in size. Microfiche are stored in open-top envelopes which are put in drawers or boxes as file cards, or fitted into pockets in purpose-made books.
Normally microfilming uses high resolution panchromatic monochrome stock. Positive color film giving good reproduction and high resolution can also be used. Roll film is provided 16, 35 and 105 mm wide in lengths of 30 metres (100 ft) and longer, and is usually unperforated. Roll film is developed, fixed and washed by continuous processors.
The simplest microfilm camera that is still in use is a rail mounted structure at the top of which is a bellows camera for 105 x 148 mm film. A frame or copy board holds the original drawing vertical. The camera has a horizontal axis which passes through the center of the copy. The structure may be moved horizontally on rails.
A camera is built into a box. In some versions this is for bench top use, other versions are portable. The operator maintains a stack of material to be filmed in a tray, the camera automatically takes one document after another for advancement through the machine. The camera lens sees the documents as they pass a slot. Film behind the lens advances exactly with the image.