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1945 Theatre Catalog, 4th Edition, Page 331 (307)

1945 Theatre Catalog, 4th Edition
1945 Theatre Catalog
1945 Theatre Catalog, 4th Edition, Page 331
Page 331

1945 Theatre Catalog, 4th Edition, Page 331

jector. It is not first ground to dimensions and then submitted to a hardening process which may warp the delicate exactness of those dimensions. Now it is obviously more expensive to grind hardened metal than soft metal. International Projector Corporation does not go to that expense without reason. The reason is that experience has shown grinding after hardening gives a steadier screen image. Additionally, this method of hardening gives longer wear.

The above may besconsidered typical of an immense number of details, each small in itself, that contribute to producing a steady pictu1'%or the reverse. In the case of the intermittent movement which drives the sprocket just referred to: 13 different points on the star wheel are ground to an accuracy of 1/10,000 inch. At the same time, experience proves it is equally important not to have such close fit at other points. Here again their vast background of experience guides IPC technicians in selecting the one best procedure, having in mind not only the excellence of the immediate results, but the durability of that excellence through years of gruelling operation.

Again, in the gear train, Simplex E-7 design features hunting-tooth gearing, which means simply that the same two teeth do not mesh at every revolution. If they did, high spots would inevitably develop, and every time ,a high spot came around the picture would jump a little on the screen. With hunting-tooth gearing a given tooth on one gear meshes with a different tooth on the mating gear at each revolution. High spots can not appear.

Another small but vital detail is the cushioning of the gear train against the unavoidable vibration resulting from the start-stop-start-stop nature of the intermittent action. For this purpose,'Simplex E-7 designers introduced a shock-proof gear, composed partly of resilient material. This material takes up and cushions the vibration from the intermittent movement, minimizing the chance that this vibration will appear on the screen as picture jump.

If the picture is to be steady, it is also necessary to hold and position the film very accurately while it is in the gate. But film sometimes varies in thickness. Therefore best results can be obtained only if the gate pad tension is adjustable. In the Simplex E-7 cone-shaped springs apply equal tension to the pads bearing against both edges of the film; this pressure can be adjusted at any time, in a second or so, without tools, and while the film is running. Each adjustment will apply, automatically and inherentlv, to both edges of the film alike; and when it is completed it can be locked down without tools.

In their ardent and experience-guided search for the one best way of meeting every mechanical problem related to steadiness of the screen image, Simplex E-7 designers believe they have been successful, and very proudly point to the proofea vertical jump of less than 1/8 inch per 12-foot screen picture.

Horizontal unsteadiness, or weaving. presents a less difiicult problem, but of course, also, must be controlled. Simplex designers here drew on their Vc'l'y extensive experience with Hollywood equip l945-THEATIE


ment and fitted the E-7 with studiovtype guides of the same nature as those used in the camera.

Screen Brightness

The picture must be bright as well as steady. Simplex was the first manufacturer to introduce double shutters. Twenty-four frames, or stills, are projected each second; each one is exposed twice, making 48 exposures a second; each exposure involves one transition from a darkened to an illuminated screen and one from illumination to darknesse96 transitions between light and darkness in each second of operation. Use of double shutters, pioneered by Simplex, causes the area of light to appear first at the center of the screen and spread toward top and bottom; similarly regions of darkness appear at top and bottom and meet at the center. Not only is this itdissolving effectii more pleasing to the eye, but the 96 transitions a second take only half as long to complete. The shutter blades can therefore be made narrower; 70 instead of 90 degrees. The period of total screen illumination is lengthened accordingly; the increase in the illumination and therefore in the brightness of the picture is 20 per cent.

Cleanliness of the Picture

One important cause of dullness in the screen image may be the presence of a layer of lubricating oil on film, or lenses. The one-shot lubricating system of the E-7 has a number of striking advantages; among them, that oil does not get on film or lenses. It is confined to a system that is completely closed, so far as the film side of the projector is concerned; it is applied under pressure to each bearing in the exact quantity that hearing needs, with no excess. Cleanliness of the image is further enhanced by provisions against dirt, and these provisions also reduce the possibility of the film being scratched by dirt.

Among other protections against a dirty picture are, for example, the ease with which both film gate and film trap can be removed. The gate can be taken out without tools, and in a few seconds. It can be replaced as readily. The trap is also removable in a few seconds, with only a screwdriver and the loosening of two screws. The film, of course, passes between gate and trap. Loose dirt in that location can get into the light path and be projected as shadows on the screen. This also is one of the places in the mechanism where the film is most


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1945 Theatre Catalog, 4th Edition, Page 331