International projectionist (Jan-Dec 1958)

the tendency toward film deformation. The pulsed air buckle correction method was tried in a number of installations and showed very promising results. However, several variables, such as film history and its condition, different light levels, and air-line pressure changes made operation unreliable and inconsistent. The air-jet noise also was considered objectionable in some projection rooms. Improved Equipment Improved picture quality could be obtained with pulsed air, but the displacement of the perfect focus position from center to side of the frame was too large to allow the full benefit of improved definition over the entire screen. In these experiments, good focus was sometimes difficult to obtain at PUL L DOWN FUCKER BLADE AV. FOCUS STRAIGHT GATE FIG. 2. Oscilloscope trace of buckle move mcnr Straight gate. the early instant of the first exposure. This poor focus condition was not due to travel ghost. There was a possibility that it could be caused by some unexplained prior film action during pull-down, the dark part of the cycle, which could not be observed with the equipment used. The stroboscopic measuring device could, of course, show only film positions while the two open shutter sectors admitted light to the screen. A different method was therefore worked out to keep "in touch" with the rapidly moving surface of each film frame in the aperture. A mechanoelectrical transducer (RCA Type 5734) was employed in the new equipment. The transducer is a triode vacuum tube in which the plate is carried by a rigid shaft extending through a flexible diaphragm to the outside of the tube. An extension of this plate shaft, a feeler wire, rests on the film in the center of the aperture. Any movement of the film frame in the direction of the optical axis is thus translated into a displacement between the fixed grid and the movable plate of the triode, with a proportional change in plate current. FIG. 3. Probable strain patterns in film at end of pulldown. An oscilloscope triggered synchronously at the film frame rate, displays a curve very similar to that obtained by the stroboscope method, and in addition, extends into the dark periods, when the shutter blades obscure the screen. Analysis of Results A photograph of the buckle movements on an oscilloscope screen is shown in Fig. 2. This is for black-andwhite film in a conventional straight projector gate. It shows the first exposure, then the light cut off by the flicker blade which stops the negative excursion, until light strikes the film again with the second exposure. The upper horizontal line, just above the zero line, indicates the running film plane position without light, that is, with lamphouse dowser closed. At the left of the photograph, in the section marked "Pull Down," note the steep return toward the zero position as the new, fresh frame enters the gate. The new film frame is not at rest, however, even though no light has yet hit it, and no energy has been absorbed. It appears as if a fluttering motion violently shakes the new film frame beyond both sides of the zero position, and this movement reaches into the beginning of the first exposure. This same phenomenon was observed by Carver, Talbot and Loomis of Eastman Kodak Co. in some sections of the high-speed film on film buckling made at their laboratory and shown to the Society in 1943. It is believed that a strain pattern exists in the length of film in the pro jector gate, down to the intermittent sprocket. In Fig. 3, we have tried to illustrate the pattern set up by the forces of pulldown, holdback friction and film inertia between perforation edges. Curved Gate The above discussed defects in the projection phase, which are responsible for a serious amount of degradation in the overall system of motion pictures, led to an investigation of the curved film gate as a means of stiffen "■iii^ik: rr7fc& SECTION A A FIG. 4. Attitude of film in curved gate. ing the film and of restraining these undesirable film frame motions. Fig. 4 shows the attitude of the curved film with respect to the projection lens. It conforms with the curvature of field of the projection lens. The upper drawing, Section AA, shows the film (broken line) as it enters the curved gate at the aperture, at the beginning of the first exposure. Note that it is curled toward the lens, that is, positive. [TO BE CONCLUDED] Novel 'Solion' Integrator Replacement for radio tubes and transistors which could cut weight, size, cost of airlines' navigation equipment, may be a new electrochemical device, the solion, says Navy's Ordnance Laboratory. One type, a 20x/2 x % inch integrator unit, is small cylinder divided by a porous ceramic filter with electrodes immersed in iodine-containing potassium iodide soln. Low current starts integrator ; changes in temperature, pressure, light, sound, acceleration caused by airplane movements keep unit producing current. \A INTERNATIONAL PROJECTIONIST • JUNE 1958