Motion Picture News (Mar-Apr 1923)

1484 Motion Picture News DEBRIE CAMERAS SLOW MOTION ORD EVENTS OF THE WORLD The Debrie High Speed Camera is capable of taking as high as 240 pictures per second for analyzing rapid motion. Of metal construction and weighs only 22 lbs., dimensions iyA" long, 6y2" wide and 8" high, carries an outside double magazine of 400 foot capacity. MOTION PICTURC APPARATUS CO. P INCORPORATED Lb 118 West 44th Street New York City Opposite Belasco Theatre Ownership Management of WlUouffhby. Inc. Fundamentals of Light {Continued from page 1478) image depending upon the refraction of light. But before taking up the consideration of this important piece of apparatus for photo Fig. 20 — A cross section of a photographic objective, one of the combinations consisting of uncemented elements and the other of cemented lenses graphic work it will be necessary to explain what we mean by the " Optics of Photography" as distinguished from the optics of other sciences, such as those of the telescope and the microscope. The chief distinctions are of two kinds: 1st, in photographic optics the lens must be capable of transmitting and bringing to a focus in the same plane oblique and axial rays of light, as shown in Fig. 20. The principal lens or objective of the telescope will not give a sharp image of an object if removed a slight degree from the axis or perfect squareness of position in relation to the line of light. Hence, the sharpness of the image produced by the objective of the telescope is confined to a small area close to the axis. The photographic lens, on the other hand, must be so constructed that it will give a sharp image of objects in front of the center of the lens and also of those that are situated to a certain extent on each side of the center. 2d. The photographic lens must also be so constructed that it will bring to a focus at the same spot the chemical and visual rays of light. If not corrected, the lens will act as a prism and separate the light into its component parts and produce the spectral or rainbow fringe around the edges of the image. The violet or active end of the spectrum is brought to a focus close to the lens and the red at the greatest distance. The yellow, which is brightest visually, is also further from the lens than the active violet. In focusing visually, the plane of the yellow would be sharp, but in photographing the sensitive surface would have to occupy the plane of the violet. The result would be that the image of the object focused by the eye would be a blur in the photograph. The photographic lens must be so constructed that the image of the object will appear sharp and clearly defined to the eye, and be equally sharp as a result of the chemical rays, when it is developed upon the photographic plate. Such a coincidence of the chemical and visual rays Fig. 21 — A. B. C. positive or converging lenses. D. E. F. negative or diverging lenses. A, double convex; B, plano-convex ; C, convexo-concave or meniscus; D, double concave; E, plano-concave; F, concave-convex does not exist in the telescope or the microscope, but only in the photographic lens. In the telescope and the microscope, which are constructed for visual work, it is not necessary. To sum up these remarks it can be stated briefly that photographic lenses transmit oblique as well as axial rays and bring them to a focus in the same plane ; and also to bring the chemical and visual rays of light to a focus at the same spot. {Continued on page 1486) Fig. 23 — Nodal point outside the lens. Fig. 22— Nodal point vnihin the lens LIBMAN-SPANJER corp. BUILDERS OF LOBBY FRAMES DE LUXE CHANGEABLE SIGNS TICKET BOOTHS TICKET BOXES FOYER LAMPS, ETC. Factory: Office: Factory: NEWARK, N. J. NEW YORK CHICAGO, ILL.