International projectionist (Jan-Dec 1954)

AN EVALUATION OF OPTICAL SOUND (Continued from page 8) film produce less noticeable noises. In Europe, however, very narrow slit-images are preferred. Most European soundhead manufacturers use images approximately 8 mils (20 microns) in width, and the German firm of Zeiss Ikon employs a 7-mil (18-micron) slit-image in Ernemann equipment. This writer sees no need for such narrow images. The American 1^-mil slit-image, adopted as a standard by the Academy of Motion Picture Arts and Sciences, has everything to recommend it. In every case the length of the slit SELECTIFIERSi AMERICAN SELECTIFIER DIV. . SELECT-A-VOLTAGE ' SELENIUM RECTIFIERS { A "SINGLE " OK FOR 2 ARCS! "Superior" & "50,000 Hour" types, | 50 to 400 Amps, rugged, oversized, selenium stacks. Adjustable-in-use 1 glass insulated transformers. Operate continuously in any climate, at i standard or heavy overloads at maximum efficiency on both i "Suprex" and H.I. Arcs. 1 SELECTIFIERS sell themselves on obvious quality and dependability. ^Siii^^ " i (Hmii^mBS Write: Doc Faige \j''m-\ II NORPAT, INC. 113 W. 42 St. 1 ,-'>iiiMmnV' N. Y. C. 36 il image is 0.084 inch (2.13 millimeters), slightly less than the width of the printed area of the track (0.1 in., or 2.54 mm. ) . The width of the sound record in a completely modulated variable-area track is the same as the length of the scanning beam. Only the loudest sounds have a modulation as great as this. Focusing a Delicate Job Every projectionist knows that the quality of the sound is poor when the optical tube is out of focus. The focusing procedure, though simple, is a delicate job. It can't be hurried. By running a 9,000-cycle test loop and plugging an output meter into the soundhead or preamplifier, the sound service engineer lines up the rotational, or azimuthal, adjustment of the tube. ( The thin line of light must cut the track perpendicularly to the direction of film-travel.) Then he restores the focus by moving the tube nearer or farther away from the film-plane. In each case the needle of the output meter shows when the output is at maximum strength. The projectionist can use the "flicker test" for focusing the optical unit, but he must guard against disturbing the rotational adjustment. If the scanning beam cuts the track at a slant, distortion will be produced. Procedure for Test Thread a short length of film having a high-frequency record ( many very fine lines) into the soundhead. With the exciter turned on, and with a white card placed in front of the photocell so that the exciting light forms a spot on it, "inch" the film down very slowly by means of the projector handwheel. The soundtrack ARE YOU CONVERTING TO CINemaScoPC frequency lines will throw shadows on the card. If the shadows move upward, the optical tube should be farther from the film: if the shadows move downward ( in the same direction that the film moves), the tube should be closer to the film. When the unit is in perfect focus, the spot of light on the card will flicker uniformly as the film moves down through the beam. Lateral adjustment of the sound s PUCES ^^ NOT y HOLDING Film breaks are costly. Play safe by using JEFRONA All-purpose CEMENT Has greater adhesive qualities. Don't take our word for it. Send for FREE sample and judge for yourself. CAMERA EQUIPMENT CO. DEPT. J-6-8 1600 Broadway New York 19, N. Y. AH UHCONmiOHAl GUARANm • ^nom 9^ INTERNATIONAL PROJECTIONIST WtONE ^ The NEW HI-LUX SCREEN has reached a state of perfection that will meet the most EXACTING PROJECTION requirements |T| SEAMLESS CONSTRUCTION [2] UNIFORMITY OF SURFACE [3] SHARP DEFINITION QEVEN DISTRIBUTION TO ALL USEFUL ANGLES... \S\ TEAR-PROOF CONSTRUCTION We bnfk those i-lainis irith a ■^ ntonfu-hafk tiuiirantft' and ifou, ^ .Wf. KxhibiHtr. arv Iht' jutlt/v: mflTTAME SCREEN CORPORATION ■»*• ■ l^rB^K 165ClermontA»e.,B.klyn,N.r. Mid-West Offlce-L. E. Cooley • 408 S. Oak Park Ave.. Oak Park. III. 33