International projectionist (Jan-Dec 1954)

for IP, the Tushinsky device accomplished the purpose for which it was intended — the showing of motion pictures in all aspect ratios within the range mentioned previously. However, at this showing we used a CinemaScope black-and-white test-pattern film, having both horizontal and vertical lines. Alternate projectors were used to show the difference in both focus and light level between the Bausch & Lomb CinemaScope lens and the Tushinsky prismatic attachment. Considerable Light Loss Much to our surprise, the focus of the Tushinsky anamorphic attachment was good and in every respect comparable to that attained by the B. & L. CinemaScope lens. But we were surprised to note that as between the B. & L. CinemaScope lens and the Tushinsky unit there was, to our eyes, a light loss with the Tushinsky unit of approximately 45% ! Now, this was rather an astonishing spectacle, since we couldn't conceive how a rather simple prismatic device employing only two optical elements could possibly induce such a large degree of light-transmission loss. In all fairness to Tushinsky, it must be stated that his effective aperture opening was only 3 %", while the projection lens was 4" in diameter. This would naturally have the effect of cutting down his light by reason of his reduced "working" aperture. IP understands that a larger effective aperture will be employed in the Tushinsky unit in the very near future to accomo date the present 4" diameter lens mounts. This could make a whale of a difference. Eminent Optical Opinion The light loss occasioned by the use of the Tushinsky unit prompted IP to consult eminent optical authorities. Several theories relative to the action of optical anamorphic prisms, and the possible reasons for light loss, were advanced, as follows: 1. The angle at which the light beam strikes the prism may occasion considerable dispersion and absorption of light within the housing. 2. The effective aperture of such a device should be fully equal to that of the projection lens so that it can accept the full light output from the latter. 3. Extremely accurate positioning of the optical elements within the housing, which is, of course, a mechanical manufacturing procedure. 4. Possible desirability of matching the optics of such a unit with those of the projection lens being used. 5. The speed of the regular projection lens would, if of a "fast" character, naturally magnify any inherent errors in the attached unit. Two Vital Field Problems There are other factors to be considered in connection with the use of prismatic anamorphic devices such as the Tushinsky unit. First and most important is the quality of the glass used. Next is the positioning of the elements within the housing — a Lens Pre-Focusing Device A calibrated device which enables the projectionist to pre-focus a variety of different lenses has been designed by Joe Tritsch, member of Los Angeles Local 150 and projectionist at the Encino Theatre, Encino, Calif. Called the "Focuset," it is a simple attachment by which the projectionist may methodically and accurately index different projector lenses in exact focus. The device consists of a dial indicator type of indexing mechanism attached to the lens holder casting in such a position that the extended or actuating position of the indexing mechanism contacts the main projector frame casting. In using the unit, a sharp image is first obtained on the screen and the position or reading of the indexing mechanism noted. Every basic position of lenses needed for various aspect ratios may consequently be determined and their position on the indicator noted. These indexing points remain valid for all subsequent lens positioning so long as neither the Focuset mounting nor the main frame casting is varied. Variable Prismatic Units 1. The angle at which the light beam strikes the prism may occasion considerable dispersion and absorption of light within the housing. 2. The effective aperture of such a device should be fully equal to that of the projection lens so that it can accept the full light output from the latter. 3. Extremely accurate positioning of the optical elements within the housing, which is, of course, a mechanical manufacturing procedure. 4. Possible desirability of matching the optics of such a unit with those of the projection lens being used. 5. The speed of the regular projection lens would, if of a "fast" character, naturally magnify any inherent errors in the attached unit. Handy lens pre-focusing device developed by Joe Trilsch, member of I A Local 150, Los Angeles, and projectionist at the Encino Theatre, Encino, Calif. question of precision manufacturing procedure. Once in the field, there arise two vitally important considerations in connection with such devices: first, theatre personnel (managers, projectionists) may attempt to exercise their personal preference for picture ratio to the extent that they use a device such as the Tushinsky unit to project a picture in a ratio in which the picture was not originally made. Gross distortion will be the inevitable result. Next, and equally important, is the fundamental necessity for cleaning any optical element. We all know that in a projection room the accumulation of dust on optical surfaces is a deterrent to good projection. This demands that optical surfaces be cleaned frequently, and this applies with especial emphasis to a device such as the Tushinsky prismatic unit. Granted that projectionists wish to clean the optical surfaces in the Tushinsky unit, the procedure would involve removing the various screws in the housing and wiping oif the prismatic lens. What is the warranty that the elements will be subsequently repositioned in proper alignment? Healthy Competitive Force With all the foregoing considerations fresh in mind, we regard the introduction of devices such as the Tushinsky unit as a healthy competitive force in the motion picture indus(Continued on page 34) 10 INTERNATIONAL PROJECTIONIST • APRIL 1954