Movie Makers (Jan-Dec 1949)

58 SINGLE FRAME CONTROLS How the simple star wheel can be adapted to your camera, for easy frame-by-frame shooting LAURENCE E. BATY, ACL SOMh mmie cameras have a device which permits the film to be advanced a single frame at a time — for animated work and other special effects. It is a good gadget, hut not widely offered. \\ ith cameras where a single frame device is not built in. The ACL Movie Book and other publications suggest that the motor release button be "tapped," lightly and quickly, thus allowing only one frame to be exposed. With the writers camera (a Cine-Kodak 8), the release button is pushed downward and something more approaching a ""blow"' was required to move it. With this method, also, the button was often driven to the lockedin running position, the tripod support was inadequate, some damage to fingernails resulted and temporary sluggishness developed in release button return. Fig. 1 ; indirectly and along a vertical path, as in Fig. 2, or indirectly along a horizontal path, as in Fig. 3. In operation, the star wheel is revolved manually by the use of a turning knob mounted on the opposite end of its shaft. DESIGN OF STAR WHEEL The design of the star wheel can be followed in Fig. 1. Each tooth should move the wear plate barely beyond the position which releases the camera motor. The root diameter of the teeth must be small enough to clear the non-running position of the wear plate. Due consideration should also be given to any angular movement of tripper arm, as in Fig. 3. To a certain extent, tolerances increase as the star wheel is made larger. THEORY OF STAR WHEEL I decided to try designing a more accurate and automatic system of single frame operation. The discussion which follows will describe my "down-button" design in detail, as well as suggesting other systems in general. Mechanical heart of my design is the simple star wheel, and the general theory of its operation is shown in Fig. ]. Mounted at the end of a suitable shaft, its teeth and hollows alternately depress and release a plate which reacts against the camera button. This reaction may be effected in a number of ways, depending on camera de FIG. 1: Star wheel action depresses • directl as camera button tour times during i 1 • each complete revolution. gested theoretically in THE COMPLETE ASSEMBLY Fig. 2 is an oblique drawing of the assembly, without detailing hubs or bearings. For simplicity, only three bearings were used: one, the bearing for the main shaft carrying the star wheel and turning knob; a second to pivot the movement of the pull rod, and a third ( rear bearing Fig. 2) to pivot the vertical action of the tripper arm. The near flange of the mounting plate — the overall design of which should be clear — was made thick to serve as bearing support. The pull rod is left long enough to accommodate the mechanism's being mounted below a titling board. The nuts which hold the pull rod in its bearing are concealed by the upper flange of the tripper arm. The upper end of the pull rod is threaded, to permit positioning of the release button bracket by means of jam nuts. The wear plate, upon which the star wheel reacts, is slotted for adjustment during assembly. (Wear compensation, incidentally, has not yet been necessary in seven years of use.) The turn knob is pinned to main shaft, and the main shaft is threaded into the star wheel. No spring was found necessary to return the pull-rod assembly following depression. [Continued on page 761 MOUNTING PLATE RELEASE BUTTON BRACKFT REAR BRG. & PIN TURN KNOB STAR WHEEL , MAIN SHAFT & BEARING ' TRIPPER ARM FIG. 2: Complete assembly of the author's single frame release for Cine-Kodak 8 is diagrammed above. Mounting plate (broken line) goes under camera and on top of tripod head. FIG. 3: Adaptation of star wheel single frame control to push-in button is seen above.