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The Projector Lens
Projector Lenses are made of optically worked glass, and are often ' 'bloomed" with a special surface coating for added brilliancy. Some are quite easy to scratch, and great care should be taken when cleaning them. Focussing is achieved by moving the lens either forwards or backwards, and is accomplished by revolving the lens or by actuating the lens mount by means of a handy screw.
Projector lenses are supplied in various focal lengths of from one to four inches, though it is quite possible to obtain others. The two-inch lens is supplied as standard with most sound projectors, and will fill an 8' 6" screen at an approximate distance of 45 feet; a picture roughly i/5th as wide as the throw.
The Shutter
The shutter consists of one or more blades attached to and revolving round a central axis, and has as its function the interruption of the projection light each time the film is moved in the gate, and also, to provide a succession of light flashes at such a rate as to prevent any flicker in the screened picture.
"Shutter ghost" is the name given to a white blurring on the screen caused by the blades of the shutter requiring adjustment, though in most projectors you will find that only one can be adjusted. This is usually the largest of three, and it should be moved either to the right or left according to whether the blurring is a top or bottom ghost. The degree of movement in adjusting will be very slight, but nevertheless, the operation is somewhat tricky, and you are advised not to attempt any such adjustments unless you are well qualified to do so. The other blades should not be tampered with as they are precision set in order to provide a flickerless picture by means of even alternations in the light for projection. Other shutters have only one blade.
The Gate and Aperture Framing
The Gate, or Film Channel, is that part of the projector wherein the film is moved by the intermittent mechanism. It includes an adjustable framing device next to the picture aperture, and allows the operator to maintain the correct alignment of the frame on the film with the frame of the aperture, and ac
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