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118 The Audio-Visual Handbook
will refer the request to a local representative, who will arrange for a demonstration.
Accessory Equipment. There are certain accessories which should be secured at the time of the purchase of the projector. First of all, no salesman should be careless enough to permit a school to purchase a projector without an extra lamp. Projection lamps will give thirty to fifty hours, or more, of satisfactory service if handled carefully and connected to the proper current. It is possible to break a lamp instantly; and if another lamp is not available, there may be several days' delay in securing one. An extra lamp is an absolute necessity and should be on hand at all times.
Additional equipment which should be on hand includes a film patching and rewinding outfit, a dustcloth, a bottle of projector oil, an extension cord, a small bottle of benzine, and a projection screen of suitable size and type. The names of companies which have such equipment available will be found on pages 219 to 221 and a discussion of the various types of screens is given on pages 124 to 128.
Care of the Film. The first essential in caring for the film is to see that the projection equipment is clean and properly adjusted; carelessness in handling the projector can cause damage to the film. The film should be run through the projector at normal speed, and such gadgets as the stop-on-film and reverse devices, which are provided on some silent projectors, should be used sparingly, or not at all. If motion is necessary to convey the message, the picture should be shown in motion and not as a combination of motion and still pictures. There are very few instances where the still projection of a motion-picture frame is advisable; in those instances the still projection should be as brief as possible to prevent damage to the film through drying or warping. In fact, there are many visual-instruction supervisors who object to any use of these devices, and film producers seldom recommend their use.
The film should be handled carefully at all times. It should be removed from the shipping can with care, and properly threaded into the projector. After it is used, it should not be rewound except for repeat showings and should be kept in the shipping can when not in use. Dust damages film quickly; therefore, precautions should be taken to protect the film.
Breaks in the film should not be repaired by amateurs, and borrowed film should be repaired only if the film is to be shown again. If repairs are made, they should be made carefully, and directly in accordance