Standard roll microfilm is either 16mm or 35mm wide (105mm roll is also widely used during the production of microfiche, but it is cut into individual A6 size sheets before use)
|Almost the entire width of microfilm is therefore available for recording images that are usually arranged in a single row along the length of the film, though two alternative layouts are common. Both alternatives feature dual rows of images. In duplex format the fronts and backs of all documents are recorded side by side across the film width. In duo format the documents run sequentially along the top row and then back down the lower row. The latter is achieved by filming one track, reversing the film in the camera, before recording the other track.|
16mm roll film is ideal for recording most office documentation, but a larger image is desirable for recording fine detail of large originals such as maps, plans, newspapers and engineering drawings. 35mm film is generally used for such applications either in roll form or as individual images set into aperture cards
|Circlips are often used to permit the easy identification, handling and loading of roll film on reels. They provide dust protection, a flat surface for labelling and facilitate rapid threading of film into a reader or reader-printer. They are almost universally employed with automated image retrieval systems based on roll formats. The design of the circlip has been standardised to permit films to be exchanged between equipment from different sources.|
Image retrieval from 16mm roll film frequently relies on counting small marks (blips) filmed below the images.
Somewhat similar in appearance to microfiche, but differing in application, the microfilm jacket comprises rows of images cut from roll film and held in a carrier, which is usually A6 in size.
Each jacket consists of two sheets of thin clear plastic cemented or welded together at intervals to produce channels into which strips, or even single frames, of 16 or 35mm roll film can be inserted.
Because additional frames can be added at any time the system is particularly suitable for files such as customer records – a separate jacket being allocated to each customer. Combined jackets, holding both 16mm and 35mm widths also exist.