International projectionist (Oct 1931-Sept 1933)

July-August 1933 INTERNATIONAL PROJECTIONIST 13 sate for visual deficiency (astigmatism) of the observer. 5. Small Squares Target for Checking Focus (Fig. 5). — This target consists of numerous white squares, arranged and numbered in vertical and horizontal rows, against a black field. The position of the lens for which the greatest possible number of squares are projected in sharp focus is the most desirable lens position. The numbering of the squares provides a means for making comparative tests of lenses. Sound Test Section The remaining portion of the test film, some 500 feet long, is recorded on both edges, as previously stated. On one side of the film are recorded the following tests with suitable accompanying announcements : (1) Buzz track for checking the position of the scanning light relative to the sound track. (2) 6,000-cycle and 9,000-cycI/; constant frequency tracks for checking the focus of the sound optical system. (3) Selected frequencies for ascertaining the over-all characteristics, as follows: 50, 100, 200, 300, 500, 1,000, 2,000, 3,000, 4,000, 5,000, 6,000, 7,000, 8,000, 9,000, and 10,000. 1. Buzz Track. — This consists of a 300-cycle and a 1,100-cycle frequency recording, respectively, just outside the boundaries of the standard sound track area, one on each side. When the 1,100-cycle note (the higher pitched note) is heard, it indicates that the film is passing the light slit too closely to the sprocket hole margin. When the 300-cycle note (the lower pitched note) is heard, it indicates that the film is passing the light slit too closely to the picture margin. When both notes have been eliminated by properly adjusting the lateral guide rollers, or by adjusting Fig. 2. Picture-jump target the optical system, when such adjustment is provided, correct film travel path may be assumed. When one or both notes are intermittently heard, this indicates film weave. If the weaving be due to warping of the film, its effect may in some cases be reduced by adjusting the sound gate tension springs. Incorrect relative alignment of the projector head and the sound head also may cause weaving. 2. 6,000-Cycle and 9,000-Cycle Constant Frequency Tracks. — When the maximum volume of sound is obtained for each of these frequencies, it may be assumed that the optical system is correctly positioned for obtaining the best results; that is, that the scanning light is sharply focused and perpendicular to the direction of travel of the film. The 6,000 cycle note is used for making an approximate adjustment, and the 9,000-cycle note, if audible, for still finer adjustment. This positioning should not be undertaken unless the optical system has been specifically designed to be adjusted and suitable adjusting tools are available. 3. Selected Frequencies. — This track is so recorded that no voltage calibration (on a volume indicator) is required. Assuming a perfect scanning slit and a "flat" amplifier, the resulting over-all characteristics, as determined by a volume indicator, would be flat. The ear will naturally be more responsive to the 1,000-cycle note, whereas the higher and lower frequency notes will sound less loud. Of course, a volume indicator would admit of making precise measurements of the sound level ; this applies equally well to sections 2 and 3 above. On the other edge of the sound test film are recordings of voice, piano, and orchestral music. The vocal portion is to be used for testing intelligibility of speech and theatre reverberation; the piano recording for detecting flutter ("wows") ; and the orchestral recording for noting the naturalness of reproduction, which is determined by the range of frequencies reproduced by the equipment. This recording contains notes ranging from the lowest notes of the tuba and double bass to the very high overtones of the string and brass instruments. The metallic quality of special instruments, such as the wire brushes, should be particularly noticeable. Optical Alignment Tool In conjunction with the test reel, the Committee recommends a tool to be used in aligning the arc, condenser, projector aperture, and projection lens on the optical axis. The model, designed by the Committee, and referred to in the following description, conforms to the standard 13.6mm. carbons used in high-intensity lamps. To obtain the maximum illumination and most uniform distribution of light on the screen, it is of prime importance that the arc and all components of the optical system be accurately centered. Fig. 6 shows the several parts of this tool : ^ is a disk having a hole through the center, which is placed in the condenser mount instead of the condenser. ^ is a cylinder having an axial Fig. 3. Vertical line target for testing aberration of lens Fig. 4. Horizontal line target for testing aberration