It is often very useful to be able to record the image on the screen. There is a variety of methods that can be used, but the most direct is simply to photograph the screen with a 35-mm camera and color slide film. Because the screen image is refreshed every 1/30 second, it is important to use a slow shutter speed so that at least one full screen frame will have been displayed while the shutter is open. At any shutter speed greater than 1/30 second only a portion of the image will be captured. Thus, about 1/15 second is a desirable speed. For static images, even slower speeds can be used. It is also helpful to photograph the screen in a darkened room to eliminate extraneous reflections from the screen. Because most monitor screens are relatively small, the standard 50-mm focal-length lens of a 35-mm camera will produce distortion at the close distances necessary to photograph the screen. A slightly longer focal-length lens, say 100 mm to 135 mm, will eliminate any of this "pin-cushion" distortion.
Technically sophisticated camera systems are used for RGB color monitors. They photograph each of the three color signals individually to make color images on the film. In other words they first photograph the image created with the red gun, then reexpose the film to the green image, and finally make a third exposure of the blue image. Such systems produce superlative results but are also expensive. Some units cost in the range of $1000, but most cost considerably more. For the casual user, direct photography with a good 35-mm camera will usually produce more than satisfactory results.
Video cassette recorders are also excellent for recording the dynamic screen output from the microcomputer. Since the video cassette recorder is designed for use with broadcast video, the computer must provide an NTSC video signal. Recording images from the computer is easy. Plug the video output into the VCR. If a separate audio output from the computer exists, it can also be recorded by the VCR. Recording the output from an RGB video output requires specialized equipment.
Mark Wilson (1985). Drawing With Computers. Perigee Books, pp. 24-25.