Moving Picture Age (Jan-Dec 1922)

20 MOVING PICTURE AGE April, 1922 TABLE III Floor Plan of Typical Theatre with an Extreme Angle of 40 Degrees; 95 Per Cent of the Seats Lie within an Angle of 30 Degrees In selecting a screen for a motion-picture auditorium, the procedure should be somewhat as follows : First, determine from the floor plan the maximum angle of view. Let us suppose that this angle is found to be 30 degrees. In Table II will be found a list of commercial projection screens and in the second column the maximum angle for each screen is given. It would be undesirable to use a screen for which the maximum angle is 20 degrees, in a 30-degree auditorium, so we may rule out the first few secreens, which are listed as being suitable only to an angle of 20 degrees. It will then be noticed that any of the remaining screens may be used without exceeding the angle for which they become unsatisfactory. If there were no other factors to consider, the most efficient screen would be the one that had the highest average reflecting power. The values of the average reflecting power will be found in column 3. A low reflecting power is undesirable, since it necessitates a larger electric current through the arc or a more powerful incandescent lamp in the projection machine, and therefore increases the cost of operation. Please note that the list of screens given herewith is by no means complete. It covers only those screens that were used in the Research Laboratory tests. Other screens should also be considered, and makers of such screens can be called upon for suitable data for purposes of comparison. There are several other factors, however, of as much importance as a high reflecting power. The texture and color must also be considered in choosing a projection screen. These factors are listed in columns 4 and 5 of Table II. It is, of course, difficult to describe the color texture in exact terms. Samples that could be described by the same terms may appear very different when placed side by side. Columns 4 and 5 must be considered, therefore, as of value in giving only a very general idea of the character of the surface of the screen. The Research Laboratory reports that it is not in a position to advise on two other factors that will influence the choice of a screen, namely, the durability and the cost. The problem undertaken by the laboratory was to determine the most satisfactory conditions of projection, regardless of their cost. It is believed, however, that improvements as suggested in the foregoing will soon be reflected in a more satisfied audience. The Eastman Kodak Company is prepared to measure the reflection characteristics of samples of motion-picture screens, and a testing department is maintained at the Research Laboratory for this purpose. A sample screen eight inches square is required. The company is also ready at any time to co-operate in the choice of a suitable screen to fit a given theatre. A nominal charge only is made for such services. All correspondence or samples of screens should be addressed to the Motion Picture Film Department, Eastman Kodak Company, Rochester, New York. After measuring the reflection characteristics of various motion-picture projection screens, it was decided to examine a number of miscellaneous surfaces. It was thought that an examination of their characteristics might point the way to the manufacture of even better and more efficient screens than at present. The results of this examination are given in Table III, which is similar to Table II for the commercial projection screens. No. Maximum Angle Reflecting Power 21 20° 339 22 20° 305 23 70° 94 24 70° 82 25 70° 75 26 70° 74 27 70° 67 28 29 70° 70° 62 49 Surface Focusing Screen and Mirror Sand blasted Mirror Magnesium Carbonate (Chalk) Photo-Stock Coated Opal Glass White Drawing Paper Photo-Stock Uncoated White Blotting Paper Sand blasted Aluminum It will be noted that only two of the miscellaneous surfaces fall in the 20-degree class, and the rest in the 70-degree class. The surfaces numbered "21" and "22" are quite similar, and are not suited for use beyond 20 degrees. No. 21 is prepared by placing a mirror directly behind a ground-glass focusing screen, while No. 22 is a mirror, the first surface of which had been sand-blasted. In the 70-degree class the surface of chalk (magnesium carbonate) is the most interesting. The reflecting power is high and very nearly constant out to 70 degrees. It has a pure white color and a surface that appears perfectly smooth to the eye. For this reason scientists have adopted this surface as the standard of a diffusely reflecting substance, although it would naturally be unsuited as a projection screen. The actual values of the reflecting powers of all substances are given in Table IV for all angles of observation at which measurements were made. The reflecting power was measured by comparing the brightness of the surface being examined to that of a surface of magnesium carbonate viewed perpendicularly under the same conditions of illumination. The reflecting power of the magnesium carbonate was assumed to be 100, and the reflecting powers of the other substances referred thereto. TABLE IV Angle No. 0° 5° 10° 15° 20° 30° 40° 50° 60° 70° 1 268 256 215 168 120 64.8 34.3 21.8 16.8 14.2 2 300 264 255 206 167 93.9 52.2 26.5 17.0 13.3 3 208 203 188 161 134 85.0 53.3 33.0 22.4 18.3 4 177 174 165 143 122 85.9 63.0 33.0 23.8 17.7 5 72 9 72 2 70.8 70.5 69.4 68.9 68.1 68.8 67.0 64.0 6 286 273 229 173 129 66.0 33.0 21.4 15.2 13.7 7 311 288 234 180 125 66.0 35.0 21.7 15.6 14.0 8 230 200 200 171 141 63.1 47.4 29.6 20.3 16.0 9 208 197 177 152 127 80.6 47.9 34.3 24.3 19.9 10 186 183 169 146 120 79.8 47.9 31.3 22.2 17.6 11 66 4 66 3 65.2 63.6 £2.4 61.0 60.4 60.0 59.3 58.9 12 164 151 136 112 97.0 75.1 56.0 52.9 47.0 43.0 13 193 187 154 124 98.5 72.2 56.4 30.2 43.2 40.9 14 142 137 122 103 93.6 76.4 63.7 55.6 50.6 46.6 IB 71. 7 71 7' 70.6 69.9 69.2 63.6 67.1 66.0 . 65.3 64.8 16 126 120 116 104 90.7 68.8 47.1 34.3 26.5 21.9 17 183 172 157 134 107 65.0 42.1 26.8 20.9 16.8 ie 292 271 216 160 108 49.2 28.4 17.4 13.1 9.7 19 78. 6 78. 6 74.9 73.3 71.1 68.6 65.3 63.9 62.3 59.5 20 148 136 111 93.6 74.1 50.2 34.1 26.6 22.6 19.5 21 460 430 373 267 176 73.3 31.9 20.6 19.0 19.4 22 473 399 297 224 121 62.0 40.2 34.2 32.0 31.1 23 100 100 99.9 98.0 96.9 94.9 92.4 89.5 84.8 76.8 24 91 1 88. 0 84.9 e2.5 80.5 79.3 78.7 76.7 76.9 74.3 25 77 1 77 1 76.0 76.0 74.8 73.7 73.7 72.6 70.5 68.2 2« 82 7 82 7 81.5 77.8 74.4 72.0 69.5 63.3 67.6 66.4 27 73 9 73 9 71.2 70.0 67.0 65.0 63.5 62.2 61.1 58.4 2B 68. 9 67 9 65.9 64.0 63.0 60.8 59.7 57.2 54.6 54.2 29 66 J 64 1 61.4 57.6 52.4 45.5 40.1 36.0 35.3 32.6 A CORRECTION ALTHOUGH we obtained the drawing of the safety-standard film dimensions, which appeared in the February issue, from the Society of Motion Picture Engineers and naturally assumed that it was the correct drawing, it appears that a change was subsequently made in the sizes of this film. Perhaps it is best to quote a letter received from Mr. Willard B. Cook, secretary of the Associated Manufacturers of Safety Standard Films and Projectors, as follows: I should like to call your attention to the dimensions that you published of safety-standard film. The cut that you published was the one originally proposed by Mr. Victor at the meeting of the Society of Motion Picture Engineers, held in Rochester in April, 1918, and embodied the dimensions which he had scaled from an old piece of Pathescope film. Unfortunately the dimensions proposed were not quite correct, and the first films made in accordance therewith by the Eastman Kodak Company were found to be hopelessly mutilated when used on existing Pathescope machines. Therefore the Eastman Company speedily altered their perforating machines to the exact pitch and dimensions of the Pathescope film, and all safety-standard film being manufactured today has the dimensions shown in the enclosed cut, and not those shown in the illustration on page 17 of the February issue of Moving Picture Age. While the error may be of very little importance, in the interest of strict accuracy it seems desirable to call your attention to it, as a new manufacturer of projectors entering the safetystandard field might adopt the dimensions shown in your cut in designing his intermittent sprocket, and later find that his projector would not give an absolutely steady screen image when he used safety-standard films. The Eastman Kodak Com