Motion Picture Herald (Jan-Mar 1956)

Mter Pwjectm A Department an FHDJECTIDIV & SDllMD Combining Projection and Anamorphic Lenses Properly by GIO GAGLIARDI CinemaScope has been with us for over two years but I venture to say that the optical reasoning and the proper operation of the projection lens with its anamorphic attachment are still not too well understood. By now we are all familiar with the fact that the anamorphic device will spread out a picture to double its size in a horizontal direction when properly aligned. Yet relatively few people in the theatre field have been interested in the principles involved, and for that reason may not be certain of the exact and proper adjustments required to obtain and maintain the best quality CinemaScope picture on the screen. The regular projection lens, Avhich is made up of spherical elements, magnifies the small picture on the film to the large image on the screen and the magnification is equal and exactly proportional to the ratio of the film dimensions. Both height and width are expanded at the same rate. However, when an anamorphic device is added to a standard lens, the width of the screen image increases at a greater rate than the height. This change of magnification rate for CinemaScope is 2-to-l. CYLINDRICAL LENS SYSTEM Anamorphic devices used for projection in the United States consist in a cylindrical lens st’stem, or in a prismatic wedge system. The former is the one originally proposed by Prof. Henri Chretien and is used in the greater number of installations and will be discussed here. The effects produced by using cylindrical mirrors has been well illustrated by the amusement parks. Most of us are familiar with the elongated or widened images re flected by these mirrors, depending upon the direction of curvature used in the mirrors. The procedure used by Chretien was somewhat similar, but it was applied to the use of accurately designed refractive cylindrical lenses. In order to produce a picture having a horizontal magnification double the vertical magnification it would have been necessary to produce a projection lens combination which should have a focal length in the horizontal plane equal to only one-half the focal length in the vertical plane. Such a lens would be almost impossible to design, or at least would be terribly complicated. ANAMORPHIC OPTICS The designer went back to the principle and simple construction of the old refractive telescope, which consisted in a converging and diverging lens, as shown in Figure 1. In this simple telescope the ratio of the focal lengths of the front and back elements is made equal to 2, and for this combination the telescopic power is equal to 2. When such a system is placed in front of a regular projection lens, it will reduce the focal length of the entire com bination to one-half its original focal length. However, in order to produce the desired anamorphic effect, the standard spherical elements of the telescopic lenses had to be changed to similar cylindrical shapes. These lenses then looked somewhat like the sketch of Figure 2. The refractive curvature of each element was active only in a hori PICTURE . . . YOURS WITH THE LIGHT OF Larger Core Area for MORE BRILLIANT ILLUMINATION and SHARPER, BRIGHTER PICTURE CiNemaScOPE VISTAVISION AND ALL OTHER WIDE SCREEN PRESENTATIONS In any lamp, on any screen, in any theatre or drive-in LORRAINE CARBONS are Longer Burning and Economical to use Amp. Volts Pos, Grade Neg. Grade 40 (I Kw) 28 42-50 55-65 70 65-70 75-80 80-85 80-90 lOO-IIO 115 115-130 130-150 135-40 150-160 170-180 31-38 3437 38 3537 39-40 37-40 50-55 5460 62 60-66 65-67 5558 68-70 68-69 7x14 7x14 8x14 8x14 9x14 9x14 9x14 9x20 10x20 10x20 1 1x20 13.6x22 13.6x18 13.6x22 13.6x22 54IC 544C 544C 514 544C 5140 544IOC 552-09 552-09 552-09 55209 55301 552-09 523 583-08 6x9 6x9 7x9 7x9 7x9 8x9 8x9 5/16x9 1/32x9 3/8x9 3/8x9 7/16x9 7/16x9 I /2x9 1/2x9 545-20C 545-C 545 C 545G 545C 545C 545C 557C 557C 557C 557C 557C 555C 555C 555C There's a Lorraine Carbon for your parficular lamp AsIc for Test Samples at Our Expense Write for your FREE NEW LORRAINE CARBON CHART of recommended amperages, voltage and arc gaps. CARBONS, Inc.BOONTON, N.J. BETTER THEATRES SECTION 15