Motion Picture Herald (Jan-Mar 1956)

mirrer and condenser systems of lamp j houses. This classification is valuable be i cause it permits the proper matching of lamp and projector optics to obtain maximum’ output. Speed Matching A great deal of discussion has developed regarding the necessity and correctness of proper matching. Since the speed of projection optical systems is a function of the angle subtended by the effective pupil of the optical unit to any given point on the film in the projector aperture, it is obvious that the center of the film frame is the only area where maximum system speeds may be obtained. For the sides and corners of the film frame, the speeds of the two systems will still be matched but will be considerably reduced. Figure 1 , page 32, shows a perfect optical match and full utilization of the speeds of a projection lens AB and a lamp condensing system EG. Angle A OB is equal to angle EOG and both serve to fill the entire lens and reflector from point 0 on the projector film gate. Figure 2, page 32, shows the same lens and reflector condition for the corner of the film gate. Here the “equivalent” aperture of the lens CB is matched to the “equivalent” aperture of the reflector IE — but, as is evident, angle CPB is smaller than the original angle A OB; therefore the speed of the lens, or of the reflector, for point P on the film gate is less than for the center. For the condition in Figure 2, it can De said that the reflector does not fill the entire lens, therefore it is acting as a stop to the full speed of the lens. This is one of the reasons why the side and corner light on the screen cannot be brought up to the same level as the center of the screen. Even when both the projector lens and the lamp optics are theoretically matched for optical speed, a few poor adjustments can very easily cut down on the total system speed. // the lamphouse is out of correct alignment, if the condensing system is in the wrong position, if the lamphouse front section is too small, if the projector rear shutter housing shields and shutter hub interfere with the full light ray, if projection lens tubes and extension shields are too long — all of these items can cause a reduction of total optical speed. At any of these points, the interference mentioned will actually serve to reduce the effective lens stop diameter and thus in effect increase the F/number of the projection lens. Measuring "Aerial Image" Accurate measurement of the lens stop diameter is a laboratory procedure ; however, it is possible to get an approximate for the PRIME LENS 8 out of 1 0 Exhibitors today choose a Kollmorgen Super Snaplite for their prime lens. Perhaps this is because for more than thirty years Snaplites have been the standard by which all other lenses have been judged. For speed, for contrast, for definition and for terrific brilliance on the screen, your 1st Choice is a Super Snaplite. Write for Bulletin 222. i^OtiCCfjC «: 0» It. «» IK Plant: ^ Northampton, Massachusetts New York Office; 30 Church Street, New York 7, N. Y. • Superior Model "A" 35mm Projectors • Superior Deluxe Bases • Superior Magazines 2000 ft. or 5000 ft. cap. • Blue Seal 35mm Optical Sound Heads • Blue Seal 4 track Stereophonic • Attachments • Complete line of Amplifiers • High Fidelity Speaker Systems BLUE SEAL SOUND DEVICES P. O. BOX 1008, NEW CANAAN. CONN. CAST IN ONE SINGLE PIECE NO WELDS • NO LINES NO STREAKS* NO CLOUDS AND TRVLY WASHABLE SEAMLESS SCREENS See your local supply center or contact us direct BODDE SCREEN Ceeipaay 11541 BRADLEY AVE.,1 THE ECONOMICAL, BUT THE FINEST, FOR WIDE-SCREEN, VISTAVISION& CINEMASCOPE Screen Samples and Literature on Request SAN FERNANDO, CALIF. better theatres Section, Guide Number of 1956 33