American Cinematographer, Volume 9 Number 10 
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Sixteen AMERICAN CINEMATOGRAPHER January, 1929 CBfor "Shootiru;" Animal Life Experts Choose the Dependable DeVry "SHOOTING" wild life with a movie camera requires above all accuracy and dependability in the camera. The opportunity for certain "shots," once missed, rarely comes again. The camera must be ready to function perfectly at the thrilling moment. Which makes it of great significance that the expert . cinematographers choose the DeVry Standard Automatic for exacting work of this character. , Pictured here are cuttings from a negative of wild life recently made by George E. Hayes, of MGM and International Newsreels, at the famous Gay Lion Farm, El Monte, California. Mr. Hayes was within three feet of the monster alligator when he obtained this superb photograph of the cavernous jaws. The dependable DeVry assures perfect pictures every time. Just point the camera and press the button. Capacity is 100 feet of standard 35 mm. film which maybe used on any scandard projector, or reduced for 16mm. projectors. Sma for free literature and detail; ahout DeVry Motion Picture equipnunt. No ohligation to you, of courJe. DEVRY CORPORATION, Dept. xi 1111 CENTER ST., CHICAGO. ILL., U.S.A. lumen per square centimeter. In a previous commun], cation to this journal it was shown that the average exposure of sound records of the variabledensity type should be at least four times this minimum value. The area of the slit used in reproducing is roughly 0.0005 square centimeter. As most photoelectric cells have a sensitivity in the neighborhood of ten mlcroamperes per lumen, the illumination at the reproducer slit should be at least 200 lumens per square centimeter to avoid operating with curr.ents less than one microampere which are difficult to amplify. Illumination in Real Optical Images The method of calculating the illumination in the case where the source is a point has already been given in equation 2. When the source is an extended surface, the illumination which it produces at a distant point is obtained by subdividing the surface into a very large number of infinitesimally small areas after the manner of the integral calculus. Each of these areas is considered to be a point and the total effect of the whole surface is found by the mathematical process known as integration. For example the illumination produced at the point P by the circular disc D of radius r in Fig. 1 is obtained by integrating equation 3 between the limits zero and (r). dE = 2nB sin a cos ada 3 The well known result of this integration is given in equation 4. E =11B sin2 a 4 When the disk is not circular, the same method is followed, but the integration is more difficult. Such cases, however, usually can be treated satisfactorily by means of the following approximation. The solid angle w within the cone of plane e is given in equation 5. w=21T(lcos9) 5 For small values of e, 2 (1 cos e) is approximately equal to sln" e. In other words, the illumination at the point P is given approximately by the product of the brightness of the disk D and the solid angle which it subtends from P as expressed by equation 6.' E ~ Bw 6 The magnitude of the solid angle in turn is determined by dividing the area of the disk D by d". Although this method is not rigorous it is a sufficiently good approximation for the present purpose and is much easier to apply in systems comprising cylindrical lenses. Let us now consider the case represented in Fig. 2. The source S having a brightness B is imaged at P by means of the lens L. From the principle of the conservation of energy, equation 4 can be shown to be applicable to this case also.e In other words, the illumination at the point P on the axis of the system depends only on the brightness of the source S and on the angle e. The effect at P is the same as though the source did not exist and the lens were a selfluminous object of the same brightness as the source. The illumination for other points on the axis to the right of the lens may be computed in similar manner by applying equation 4, the angle a, representing the angle subtended by the lens or the image P, whichever subtends the smaller angle. Sometimes slightly more illumination can be obtained at a point ahead of the image position, put it is not feasible in practice to attempt to utilize this gain because a very rapid decrease in illumination occurs at points just off the axis., 1 This effect is due in part to failure of the reciprocity law. 2 Loss of light in the optical system by absorption or reflection is here neglected and will be consistently neglected throughout this paper. The loss by absorption is generally small while the loss by reflection usually amounts to four per cent at each airglass surface. Although only a single lens is shown in Fig. 2, equation 4 obviously applies also to a more complicated optical system since it depends only on the principle of the conservation of energy. In every optical system, there is always one "aperture" which limits the axial zone pencils. This aperture may be inserted especially for the purpose, as in the case of the iris diaphragm of a
Object Description
Title  American Cinematographer, Volume 9 Number 10 
Description  Volume 9 Number 10, January 1929, pages 136. 
Subject Topical  CinematographyUnited StatesPeriodicals; American Society fo Cinematographers, Inc.Periodicals. 
Format  periodical 
Catalog Record  http://catalog.oscars.org/vwebv/holdingsInfo?bibId=25713 
Publisher  American Society of Cinematographers, Inc. 
Date  January 1929 
Source  Core Collection Periodicals 
Repository  Margaret Herrick Library, Academy of Motion Picture Arts and Sciences 
Language  English 
Rights  Public domain material. 
Description
Title  American Cinematographer, Volume 9 Number 10 
Description  Page 16 
Format  periodical 
Date  1929 
Full text  Sixteen AMERICAN CINEMATOGRAPHER January, 1929 CBfor "Shootiru;" Animal Life Experts Choose the Dependable DeVry "SHOOTING" wild life with a movie camera requires above all accuracy and dependability in the camera. The opportunity for certain "shots" once missed, rarely comes again. The camera must be ready to function perfectly at the thrilling moment. Which makes it of great significance that the expert . cinematographers choose the DeVry Standard Automatic for exacting work of this character. , Pictured here are cuttings from a negative of wild life recently made by George E. Hayes, of MGM and International Newsreels, at the famous Gay Lion Farm, El Monte, California. Mr. Hayes was within three feet of the monster alligator when he obtained this superb photograph of the cavernous jaws. The dependable DeVry assures perfect pictures every time. Just point the camera and press the button. Capacity is 100 feet of standard 35 mm. film which maybe used on any scandard projector, or reduced for 16mm. projectors. Sma for free literature and detail; ahout DeVry Motion Picture equipnunt. No ohligation to you, of courJe. DEVRY CORPORATION, Dept. xi 1111 CENTER ST., CHICAGO. ILL., U.S.A. lumen per square centimeter. In a previous commun], cation to this journal it was shown that the average exposure of sound records of the variabledensity type should be at least four times this minimum value. The area of the slit used in reproducing is roughly 0.0005 square centimeter. As most photoelectric cells have a sensitivity in the neighborhood of ten mlcroamperes per lumen, the illumination at the reproducer slit should be at least 200 lumens per square centimeter to avoid operating with curr.ents less than one microampere which are difficult to amplify. Illumination in Real Optical Images The method of calculating the illumination in the case where the source is a point has already been given in equation 2. When the source is an extended surface, the illumination which it produces at a distant point is obtained by subdividing the surface into a very large number of infinitesimally small areas after the manner of the integral calculus. Each of these areas is considered to be a point and the total effect of the whole surface is found by the mathematical process known as integration. For example the illumination produced at the point P by the circular disc D of radius r in Fig. 1 is obtained by integrating equation 3 between the limits zero and (r). dE = 2nB sin a cos ada 3 The well known result of this integration is given in equation 4. E =11B sin2 a 4 When the disk is not circular, the same method is followed, but the integration is more difficult. Such cases, however, usually can be treated satisfactorily by means of the following approximation. The solid angle w within the cone of plane e is given in equation 5. w=21T(lcos9) 5 For small values of e, 2 (1 cos e) is approximately equal to sln" e. In other words, the illumination at the point P is given approximately by the product of the brightness of the disk D and the solid angle which it subtends from P as expressed by equation 6.' E ~ Bw 6 The magnitude of the solid angle in turn is determined by dividing the area of the disk D by d". Although this method is not rigorous it is a sufficiently good approximation for the present purpose and is much easier to apply in systems comprising cylindrical lenses. Let us now consider the case represented in Fig. 2. The source S having a brightness B is imaged at P by means of the lens L. From the principle of the conservation of energy, equation 4 can be shown to be applicable to this case also.e In other words, the illumination at the point P on the axis of the system depends only on the brightness of the source S and on the angle e. The effect at P is the same as though the source did not exist and the lens were a selfluminous object of the same brightness as the source. The illumination for other points on the axis to the right of the lens may be computed in similar manner by applying equation 4, the angle a, representing the angle subtended by the lens or the image P, whichever subtends the smaller angle. Sometimes slightly more illumination can be obtained at a point ahead of the image position, put it is not feasible in practice to attempt to utilize this gain because a very rapid decrease in illumination occurs at points just off the axis., 1 This effect is due in part to failure of the reciprocity law. 2 Loss of light in the optical system by absorption or reflection is here neglected and will be consistently neglected throughout this paper. The loss by absorption is generally small while the loss by reflection usually amounts to four per cent at each airglass surface. Although only a single lens is shown in Fig. 2, equation 4 obviously applies also to a more complicated optical system since it depends only on the principle of the conservation of energy. In every optical system, there is always one "aperture" which limits the axial zone pencils. This aperture may be inserted especially for the purpose, as in the case of the iris diaphragm of a 