Selecting Equipment

In addition to cost, consider these factors in selecting microfilm equipment:
Screen size
 – The reader screen should display an entire page of information at or near the original size of the record. The screen image will be the same size as the original record if the magnification of the lens on the reader equals the reduction ratio of the microfilm. (The reduction ratio is the amount a record is reduced on film. For example, a reduction ratio of 24:1 or 16:1 means a record is reduced to 1/24 of its original size.)
An 8½ by11-inch record filmed at a reduction ratio of 24:1 will be the same size as the original when viewed on a reader with a 24X lens.
A screen smaller than the original record will display a full page from the original if the magnification of the lens on the reader is less than the reduction ratio of the microfilm. An 8½ by 11-inch record filmed at a reduction ratio of 24:1 can be viewed in its entirety on a 7¼ by 9½-inch screen if the reader has 20X magnification. The entire image will be proportionately smaller than the original.
A reader with a lens magnification greater than the reduction ratio of the microfilm will not display a full page from the original record unless the screen is proportionately larger.
Screen color
 - Neutral viewing screens are standard. They are available in tints of blue, green, and gray. Tinted screens reduce eyestrain, particularly in high-use situations.
Screen type
 - Most readers and reader/printers are the rear-projection type. They project the image from the rear of the unit onto the back of a translucent screen. Some of these screens are reversible. One side has a matte finish to reduce glare and reflections, and the other has a shiny surface for sharper images.
Unit size
 - The size of microfilm equipment varies. Small, portable readers fold into a traveling case. Desktop equipment is larger in size and most common. Larger freestanding units have many features, functions, and controls. Prices vary according to size and features.
Optics
 - Readers and reader/printers are specified by image magnification. For example, 24X means that the image is magnified 24 times. Lower-priced equipment has a fixed magnification. When selecting equipment for viewing different microforms, make sure the magnification of the equipment or lens is compatible with the reduction ratios of the microforms to be viewed. Equipment capable of handling a variety of microforms usually provides variable magnification through one of the following methods:
  • Interchangeable lenses
  • Dual lenses controlled by a lever or other mechanism
  • Zoom lenses
  • Special features. A device called a blip-chip is helpful on readers that have a motorized carriage and are used in high-retrieval situations. Electronic frame counters, or blips, are inserted on roll film as it is shot. The blip-chip reads the blips and displays the frame numbers as the motorized carriage goes through the film. When the desired frame number is displayed, the user can stop the film. (Frame numbers are identified in the index at the beginning of the film.) Most mid-priced to high-priced equipment with motorized carriages comes with a digital dis- play already installed.