Microfilm
Encyclopedia : M : MI : MIC : Microfilm
Microfilm is an analog storage medium for books, periodicals, legal documents and engineering drawings.
Its most standard form is a roll of black and white 35mm photographic film. Another form, more common for engineering drawings, is a Hollerith punch card that mounts a single exposure.
Most microfilm media have a digital indexing system exposed on the edge of each image, but these data are not required to use the microfilm, but rather to support automated retrieval systems.
Microfilm is not the most compact analog microform in wide use. Microfiche is more compact.
Advantages
The medium has numerous advantages:- First, it is compact, with far smaller storage costs than paper documents. Generally, a year of a periodical in microfilm form takes 10% of the space and 3% of the weight of its paper version.
- Second, it is lower cost than a standard subscription. Most microfilm services get a bulk discount on reproduction rights, and have lower reproduction costs than a comparable amount of printed paper.
- Third, it is a stable archival form. Most library microfilms use polyester with silver-halide dyes in hard gelatin, with an estimated life of 500 years in air-conditioning. In tropical climates with high humidity, fungus eats the gelatin used to hold silver-halide. In the tropics, diazo-based systems with shorter archival lives (20 years) are preferable, because they have polyester or epoxy surfaces.
- Fourth, since it is analog (an actual image of the original data), it is easy to view. ( much like analog phonograph records having the sound waves carved into the vinyl) Unlike digital media, the data format is instantly comprehensible to persons literate in the language; the only additional equipment that is needed is a simple magnifying glass. This reduces the possibility of incompatibility and obsolescence.
Disadvantages
The medium has numerous disadvantages:- The principal disadvantage of microfilm is that the image is too small to read with the naked eye. Special readers are required to project full-size images on a ground-glass screen or a flat reading surface.
- Hard-copy reproduction: A conventional photocopier cannot reproduce the images and a special combined scanner/printer is required. Libraries using microfilm often have a very limited number of these viewers that can produce a photocopy of an image, for a nominal fee.
- Storage space: Shelf space is required to maintain an efficient archive as well as a safe and secure storage environment.
- Actual reproduction: the microfilm itself can only be reproduced a limited number of times, while digital media do not degenerate and often include error detection and correction schemes.
Uses
Systems that mount microfilm images in punch cards have been widely used for archival storage of engineering information.For example, when airlines demand archival engineering drawings to support purchased equipment (in case the vendor goes out of business), (as of 1999) they normally specified 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.
Hollerith-mounted microfilm is roughly 3% of the size and space of conventional paper or vellum engineering drawings. Some military contracts around 1980 began to specify digital storage of engineering and maintenance data because the expenses were even lower than microfilm, but these programs are now finding it difficult to purchase new readers for the old formats.
Microfilm first saw military use during the Franco-Prussian War of 1870-71. During the Siege of Paris, the only way for the provincial government in Tours was by pigeon post, and as the pigeons could not carry paper dispatches, the Tours government turned to microfilm. Using a microphotography unit evacuated from Paris before the siege, clerks in Tours photograped paper dispatches and compressed them to microfilm, which were carried by homing pigeons into Paris and projected by magic lantern while clerks copied the dispatches onto paper. Each pigeon-load of microfilm was capable of containing up to 40,000 microphotographed dispatches.
See also
External links
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