International projectionist (Jan-Dec 1957)

nuisance. Sidesway was a source of complaint even before the commercial introduction of CinemaScope! Old-Style Flat Gates A rather large range of horizontal image movement can be expected of projector mechanisms having old-style flat gates with only a single lateral guide roller at the top of the gate. This does not mean that only old-style projectors produce annoying sidesway. however, for several modern projectors, particularly those made in Europe, have similar primitive film gates without additional means for insuring weave-free lateral guiding of the film at the aperture. Even the old Simplex Regular and Super Simplex gates, familiar to all American projectionists, and essentially unchanged since 1910, have the advantages of an effective and easily adjusted lateral guide roller with flanges of large diameter. Lateral film guiding in cameras, printers, sound recorders, and projectors involves the maintenance of a fixed lateral position of one edge of the film — the so-called "guided edge," which is the edge nearest the soundtrack. Standard film may vary in width from 35.01 mm to 34.95 mm. depending upon manufacturers' filmslitting tolerances, while a maximum degree of shrinkage in triacetate safety film of good quality (0.2%) results in a possible minimum film width of 34.88 mm. It is therefore easy to see that the edge opposite the guided edge changes its lateral positioning within an overall range of 35.01 — 34.88 = 0.13 mm when constant placement of the guided edge is successfully maintained. Correct Guiding Failure of lateral film guiding in cameras, printers, and projectors inevitably results in picture sidesway. The guided edge of film threaded in a projector is the edge nearest the projectionist as he stands at the "operating side" of the machine. It will be noticed that the guide-roller flange on the operating side is fixed, i.e. it cannot move in and out on the guideroller shaft. The opposite flange, on the other hand, is able to slide on this shaft, and is made to press in upon the non-guided edge of the film by a small coil spring. The gentle pressure afforded by this spring is sufficient to hold the guided edge of the film INTERNATIONAL PROJECTIONIST txtmbz to all ttfi friettha tfp> &twwn a (Smttngfi against the inner surface of the laterally immovable guiding flange of the lateral guide roller. The film at the guide roller, it may be assumed, is laterally very steady and exhibits little or no sidesway. Unfortunately, however, this desirable fixity of the film's lateral positioning does not extend down to the aperture, which is placed several inches below the guide roller. Why does the film fail to maintain lateral steadiness during its passage through the gate? The film is able to move from side to side upon the face of the revolving intermittent sprocket. In fact, there is more film sidesway at the sprocket than at the aperture, which is located between the intermittent sprocket and the lateral guide roller. The range of sidesway upon the intermittent sprocket is limited by the sprocket shoe whose sides contact the edges of the film during its sidewise oscillations. The flanged guide roller at the top of the gate is thereby forced to act as the "fulcrum" of sidesway, the flexible upper loop permitting the rapidly travelling film to oscillate back and forth above the guide roller. Guide Roller "Pivot" The guide roller, then, acts as a sort of "pivot" which allows the film in the gate to swing from side to side on the face of the revolving intermittent sprocket. Because the aperture is fairly close to the sprocket, the sideweaving movements of the film show up rather prominently on the screen. Increasing the tension of the movable guide-roller flange does not reduce sidesway. Indeed, such an increase of pressure on the edges of the film may make matters much worse by buckling the film and causing the upper loop to flop. The film always has a tendency to "pinch out" at the guide roller when flange tension is too great. Flange tension should therefore be very gentle to steady the motion of the film as much as possible. Projectionists should not hesitate to reduce flange tension when the film is seen to flutter violently between the two flanges of the guide roller. This is an especially important matter in the successful operation of Simplex Regular, Super Simplex, and Century mechanisms. It may not be possible to eliminate sidesway completely from these machines, but very much can be done to reduce it to the point where it is not too troublesome even during the projection of CinemaScope prints with anamorphic lenses. European Projectors Certain European projectors are frequently criticized on the score of side-weave. As we pointed out, the film gates of many of these machines are rather primitive and do not permit the full advantages of superb European intermittent movements to be realized. Even the most carefully constructed European mechanisms imported into the United States for special widefilm processes exhibit an astonishing absence of engineering judgment as regards the length and general design of the film gate. A gate having runners scarcely 3 inches long, and without large-flanged edge-guiding rollers, is obviously inadequate for the projection of 70-mm film. Wide-film Todd-AO showings are marred by a degree of sidesway far in excess of the amount which we are willing to accept in 35-mm projection. Even though the projectionist himself, can minimize sidesway by careful adjustment of gate and guide-roller parts, the complete elimination of INTERNATIONAL PROJECTIONIST • DECEMBER 1957