Journal of the Society of Motion Picture and Television Engineers (1950-1954)

endent prisms, the 90° angle is fixed y centrifugal force at exactly the same blue as the angle between the correkonding two surfaces in the notched gaining sectors. As these notches are Si cut with the same tool, it has proved ossible to maintain the 90° angle with much greater precision than ±15 lin. The separation between the two iperposed images on the film is thereby reatly reduced. In the older Isotran camera, the ^fleeting prisms are carried on the mer surface of a ledge, alongside the hotosensitive film. Light from the bjective lens is reflected from the risms directly across the rotating disk, irough the two refocusing lenses, to ic photosensitive film surface at the pposite side. With this arrangement, is necessary that the prisms be set n the inner surface of the ledge with lie lines of intersection of the mutually •erpendicular reflecting surfaces at a onsiderable angle to the axis of spin of le disk. The motion of the prisms irough the light beam from the objecve lens includes a component of rotaon about the optical axis of that lens, ""his rotational component of the prism aotion imparts a rotation to the final mage on the film. This aberration as been eliminated in the new Isotran amera by the mounting of the reectors on the outer periphery of the isk, with the lines of intersection of the nutually perpendicular reflecting suraces parallel to the axis of spin of the isk. In the older Isotran design, with noving prisms of triangular cross section, 11 rays of light pass through one glass-air urface of the prism twice in order to each and to return from the reflecting urfaces. Upon each passage through lis surface, part of the light is reflected nd reaches the film to form a stationary .nal image, uncompensated for film novement. Consequently, highlights re sometimes recorded as longitudinal treaks across the film. This condition has been alleviated in the new Isotran design, in which no transmission through glass is involved in the image-transport mechanism at the outer periphery of the spinning disk. The cylindrical lens located near the plane of the primary image of the new Isotran camera reflects part of the light beam, just as do the surfaces of the moving prisms in the older design. However, this reflected light is not brought to such an undesirably sharp focus on the film, and for the most part it falls alongside the film rather than on the film. Mechanical Design The camera is 80 in. long, 32 in. wide, and 35 in. high. The axis of the objective lens of the present optical system is in the same vertical plane as the axis of spin of the disk, and is inclined 12j° to the vertical. With an external mirror above the objective lens, the horizontal line of view is 38 in. above the floor. External connections are made to a 220-v, 3-phase, power source for driving the motor. Also, an electrical circuit is provided for tripping the shutter above the objective lens, which limits the overall time of operation to a single rotation of the disk. A 3-hp Stocks vacuum pump has proved very satisfactory to evacuate the chamber to minimize windage losses. It provides a 25-in. vacuum within the housings for the rotating disk and the hydraulic piston motor within a few seconds. The spinning disk, machined from a forging of aluminum alloy, was designed for service up to 12,000 rpm, corresponding to 100,000 frames/sec. The rough forged blank for this disk was supplied by the Aluminum Company of America. The material, 14S-T61, has a certified yield strength of 61,500 psi, with 12% elongation. After forging, the blank received a primary heat treatment, rough machining, a final heat treatment, and finish machining. The forging was checked by ultrasonics and found free Miller and Scharf: Isotransport Camera 139