Types of Microform
Microforms are scaled down reproductions of documents either films or paper, made for the purpose of storage, reading, printing and transmission. They are literally micro forms of the documents. Usually microform images are are reduced about a twenty-fifth of the original document. They may be positives or negatives and the most common of thee are Microfilm, Microfiche and Aperture Cards.
Microfiche can be found on a sheet of flat film, around paper size A6. This sheet is a matrix of micro images. The frames maybe landscape or portrait in orientation and along the top of the microfiche, a title maybe recorded for visual identification.
16m & 35mm roll microfilm
Stored on open reels or put in cassettes, Microfilm is a single stream of micro images microfilm can carry 600 to 800 images and 16mm version can carry up to 10000 smaller images.
16mm Cartridge Microfilm
16mm cartridge film is typically 16mm roll microfilm in a square, plastic case or cartridge variations include the 3M cartridges, which have a metal hub with four smaller holes which often require an adapter for them to be loaded onto a scanner.
Jacket microfiche are strips of 16mm or 35mm microfilm stored in clear jackets or envelopes. Typically 4” x 6” in size the jackets can hold up to six strips of microfilm. The layout of each fiche is similar to the A6 microfiche sheets and usually includes a header strip with contents.
An aperture card is a type of punched card with a cut-out window into which a chip of microfilm is mounted. The card is typically punched with machine-readable metadata associated with the microfilm image, and printed across the top of the card for visual identification; it may also be punched by hand in the form of an edge-notched card. The microfilm chip is most commonly 35mm in height, and contains an optically reduced image, usually of some type of reference document, such as an engineering drawing.