International projectionist (Oct 1931-Sept 1933)

14 INTERNATIONAL PROJECTIONIST July-August 1933 !■■■■■■■■■■ Btaai ■■ Fig. 5. Small squares target for checking focus hole through the center, which is clamped into the projection lens holder. 5 is a short pointed bar, which is inserted through cylinder B and extended through to the aperture of the projector. The bar should be in the center of the aperture. An aperture plug having a centered circular hole with clearance for the bar can be provided as an additional convenience. Z is a pointed bar, 36 inches long and approximately ^ inch in diameter (the approximate diameter of the 13.6mm. positive carbon), which is inserted through the back of the lamp house, through the positive carbon clamp and through the disk J, which occupies the position of the condensers. This bar, which repj_aces the positive carbon, should be aligned along its entire length with the center of the condenser mount. The bar is then extended to the aperture where, by manipulating the arc housing on the base of the projector, the points of the two bars, L and S, may be aligned, as at Ji^. Subsequently to this alignment, a confirmatory test is made by drawing the long bar back toward the disk J and extending the short bar through the aperture so as to touch the point of the long bar as indicated at t?, Further manipulation of the arc housing may be required before the bars are exactly aligned. After this operation, it should be possible to withdraw bar S, the smaller one, and extend bar Z through cylinder B without difficulty. (This device is a modification of a similar piece of equipment used on a limited scale some years ago. The Committee strongly -recommends a much wider use of this tool.) TT has been definitely established -* that the intensity of illumination of the screens used in most studio projection rooms is greatly in excess of the intensity that can be obtained in theaters. The great disparity that was FIG. 6 An optical alignment tool in use found to exist was pointed out in a report of the Theatre Lighting Committee, published in the February, 1931, issue of the Joitrnal. Complaints regarding dense prints still persist, however, indicating the need for additional emphasis in the matter. The Projection Practice Committee has conducted a partial survey of typical theaters for the purpose of determining the values of screen illumination obtaining in practice, and it is significant that its findings, in a widely separated territory and after a lapse of two years, check closely with the findings of the Theater Lighting Committee referred to previously. The results of these two independent surveys indicate that the average intensity of the projected light at the surface of theater screens lies between 8 and 12 foot-candles, and that the average coefficient of reflection is about forty per cent, corresponding to intensities betwen 3.2 and 4.8 footcandles, these figures being based on the use of diffusive screens. In the tests made by this Committee, each projector was equipped with a two-blade, 90-degree shutter which caused a reduction of approximately 50 per cent of the screen illumination as compared with measurements made when the projector was at rest. In each test, the auditorium illumination approximated that obtaining during the presentation of pictures. Studio vs. Theatre Practice Invariably much smaller pictures are projected in the studio projection rooms than in the average theater, resulting in excessive screen illumination. In addition, reflective screens are sometimes used in studio rooms, adding further to the brightness of the projected picture. In the great majority of theaters, however, not only are much larger pictures projected than are shown in the studio rooms, but, in addition, diffusive screens are used. It is obvious that under such circumstances it is extremely difficult to reconcile studio "screen values" with theater "screen values," unless some compensating adjustment is made in the studio room. It seems highly desirable that no reflective screens be used in studio rooms in which print density is to be judged. On the basis of these facts, therefore, and in view of the easy and inexpensive manner in which the requisite change can be made, the Committee suggests that in each studio projection room where the screen illumination is excessive, each projector be provided with a diaphragm or iris in front of the lens to reduce the flux of projected light while measurements of screen illumination are made. The iris can be so adjusted that the screen reading approximates the average value obtaining in the theaters, after which a diaphragm mask having a fixed aperture of the proper size can be substituted at will for the iris. Change-Over Mark Location It is obviously not good practice to attract the attention of the audience to the marks used for start-motor and change-over cues. Attention will, however, be drawn to the marks if important action occurs near them. Neglect of a corresponding precaution has resulted in giving undue prominence to change-over marks in certain recent feature films. Greater care in arranging the location of the indicating marks would prevent such occurrences. The placing of indicating marks should be in accord with dt sirable practice, as follows : (1) No motion of objects directly toward or away from the mark is desirable, and (2) The marks should not be placed over moving objects or near significant action. The first requisite is that the in