The disadvantages of such a system include spatial accuracy and

film format limitations. The mechanical drum and light source drive

have inherent position noise which limit the ultimate accuracy. The

visible light source can, in general, be focused to a spot 10

micrometers in diameter. To produce a hologram on a glass plate or a

film format not compatible with the drum fixture, a second copying

process becomes necessary as with the plotters and printers. This

step is tedious and introduces further noise.

 To avoid this copy process, the plate or film can be mounted on a

flat surface and the light source scanned in both horizontal and

vertical directions. This is usually accomplished using a fixed light

source and scanning mirrors. A computer controls the source intensity

and the mirror deflection. Such a system can quickly write onto

standard film backs, including glass plates. Such two dimensional

scanners are not currently available from commercial sources but have

been produced in several labs including that of Sing Lee at the

University of California in San Diego and Roland Anderson at the

University of Florida. These scanner writers produce position

accuracies similar to that possible with the drum writers but provide

greater writing speed and flexibility.

 Another technique which is becoming popular is to use commercial

image display systems coupled with a camera. Systems such as the

DeAnza and Eyecom convert the digital information from a computer to

a raster-scan television image. This image, viewable on a normal

television monitor, is easy to see and manipulate with the computer.

The screen is then photographed with a camera mounted before the

cathode-ray tube (CRT). Several cameras, including one produced by