Cine-film projection : a practical manual for users of all types of 16-mm. (1952)

be as high as you would like it, especially in rooms or halls with a very low ceiling or where supporting beams would interfere with the top of the picture, but this sort of thing need not worry you if you have another lens with a longer focal length. Your picture would then be smaller, but being smaller it should then be possible to clear the heads of your audience. The bottom of the screened picture, even if it is only showing on the top half of the screen, must be above the heads of the audience. (Fig. 18). SCREEN LOW BEAMS ♦ B v Fig. 18 Very low beams? Then move the projector forward, and if necessary, tilt the screen as well. Note that in the diagram Mr. B. can still see the top of the screen as well as Mr. A, in spite of the fact that the screen is higher than the beams. But never have part of the audience behind the projector if you can arrange it otherwise. If a smaller picture is necessary, and you have no other lens than the one on the projector, you must bring the projector forward, for by shortening the length of throw you correspondinly shorten the width of the picture. But always fill the screen if you can, and if this is not possible, the use of black drapes, by covering the rest of the screen, will considerably improve your picture and make it easier to look at. Professional mobile operators now carry these drapes as part of their equipment, and they are always used whenever the length of the throw prevents the screen from being completely filled by the picture. The screen must be perfectly square to the audience, absolutely rigid, and so fixed that it cannot possibly sway about, and if there is a door behind it you must take care that it is closed throughout the performance, as draughts may ripple the surface and distort the picture. If the screen is set well back before a large expanse of polished 91