We use Optical Character Recognition (OCR) during our scanning and processing workflow to make the content of each page searchable. You can view the automatically generated text below as well as copy and paste individual pieces of text to quote in your own work.
Text recognition is never 100% accurate. Many parts of the scanned page may not be reflected in the OCR text output, including: images, page layout, certain fonts or handwriting.
THE PROJECTOR 223
the delicate adjustment of the whole intermittent mechanism, which moves at the terrific speed of 1,440 times per minute.
(57) Here is a very simple method of obtaining" the proper tension : adjust the gate tension so that the screen image just begins to be unsteady or the film begins to overshoot (the screen image moves up slightly) when projection speed reaches 100 feet per minute — and since today all projector motor speed is fixed at 90 feet per minute, disconnect the motor and crank the mechanism by hand. The extra ten feet of speed will allow for any variations of the braking effect on different film. If you do this, you will find the tension correct at the regular projector speed of 90 feet.
(58) Care must be exercised to prevent uneven tension where the tension is provided by two separate tension shoes, each with an independent spring. An ordinary, small postal scale will help to achieve the proper balance. First remove the letter pan. Arrange a block of wood under the two springs, so that each will strike it when pushed down a certain equal distance. Place the letter pan against the center of the shoe and press it down until it just misses contact with the wood. Note the scale reading and repeat the process on the other shoe. You will find this a reasonably accurate method of checking the tension of the two springs.
Flatness of Film Over Aperture
(59) If one conjugate foci point, of the projection lens is the film at the projector aperture and the other the screen surface, why must the film lie perfectly flat over the aperture?
One conjugate foci — that is, the optical center of the lens in relation to the film at the aperture — is very short as compared with the other — the optical center of the lens in relation to the screen— hence a very small change in its length will affect the front foci point considerably.
Suppose we now consider the surface of the film at the aperture as thousands of pinpoints, each of which