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Proposed American Standard
16mm Motion Picture Projector
For Use With Monochrome Television Film
Chains Operating on Full-Storage Basis
(Fourth Draft)
PH22.91
ture from the film chain. However, present knowledge is not sufficient to permit the formulation of a standard. 8.6 Illumination Period.
8.6.1 Definition.
8.6.1.1 The illumination period is the interval of time in which the instantaneous intensity of illumination in any part of the image area exceeds 10% of the peak instantaneous intensity.
8.6.1.2 The length of the illumination period shall be stated in terms of a percentage of V, where V is the time from the start of one television field to the start of the next field.
8.6.2 Standard. The illumination period shall not exceed 5% of V. This value is dictated by the presently accepted minimum value for the vertical blanking period of the television system, which is 5% of V.
8.6.3 Method of measurement. The illumination period shall be measured by means of a photocell, an amplifier, an oscilloscope and a timing oscillator. The photocell and amplifier must respond without saturation to the peak intensity
encountered and the frequency response of the combination shall be down not more than 3 db at 50 kc.
9. Pull-Down Period
9.1 Definition. The pull-down period is the interval of time in which film is moving through the picture aperture.
9.2 Standard. The only restriction to be placed on the pull-down period is that it shall
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never overlap any part of the illumination period.
9.2.1 If, in a particular mechanism, there is any possibility that the pulldown period may vary in phase relative to the illumination period, then the mechanism shall be designed to allow this phase to change by — 3% of V from the optimum position with no overlap of the two periods.
9.3 Method of measurement. The existence of overlap may be detected by projecting a test subject consisting of sharply defined white objects on a black background, and inspecting the projected picture for evidence of travel ghost. For this test, film complying with the requirements of American Standard Z22.541946 is recommended, although many title strips will be found quite satisfactory.
10. Phasing of Projector Relative to TV Vertical Scan
10.1 For the case of a fixed relation between pull-down and illumination periods:
10.1.1 Means shall be provided for setting the illumination period in any desired phase relative to the 60-cycle frequency which controls the phase of the motor.
10.1.2 Each time the projector is turned on, it shall re-establish this preselected phase relation by fully automatic means in less than 3 seconds.
10.1.3 During operation, the preselected phase relation shall be maintained within ± '/2% of V.
10.2 For the case of the illumination period locked to the vertical synchronizing signal and independent of the pull-down period, means shall be provided for insuring compliance with Paragraph 9.2 of this Proposed Standard.
NOT APPROVED
148
August 1952 Journal of the SMPTE Vol. 59