definition

 

 

Transparent sheet of photographic film containing microimages arranged in a grid pattern (a two-dimensional array) and having a heading that contains identifying information in text that is large enough to be read without magnification. Grid patterns vary with reduction ratios. Microfiches are grouped in five ranges of reduction ratios: low reduction (ratios up to and including 15:1), normal reduction (ratios greater than 15:1 up to and including 30:1), high reduction (ratios greater than 30:1 up to and including 60:1), very high reduction (ratios greater than 60:1 up to and including 90:1) and ultrahigh reduction (ratios greater than 90:1). The most common microfiche are made by filming textual or graphic material at a reduction ratio of approximately 24:1. Such microfiche are 105 mm. high and 148 mm. wide (approximately 4x6 in.) and have a grid pattern that accommodates 98 microimages made from documents that are no more than 11 in. high and 8 1/2 in. wide. The heading area is the width of one row and is found directly above the first row of microimages. The most common COM (Computer-Output-Microfilm) microfiche are made by recording computer-generated data at an effective reduction ratio of 48:1 on a 105 mm. x 148 mm. sheet of film. Such microfiche have a grid pattern of 15 rows and 18 columns, comprising 270 microimages. The heading area is the width of one row and is found directly above the first row of microimages. Microfiche made at ultrahigh ratios are commonly called ultrafiche. Ratios and grid patterns have not been standardized for these microfiche and differ according to application and method for production.

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