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26
15.515 " E.F. SCHMIDT
CORRECTOR PLATE FREE DIA.«2l|' MIRROR FREE DIA.= 24-Z"
60 70
PRINCIPAL FOCUS TO SCREEN
80
Fig. 1. Chart of 15.515-in. effective focal length lens operation.
Figure 2 gives a typical theater cross section showing how the projector would fit into a balcony-type house. The screen, due to the shallow depth of focus of the projector, is mounted normal to the projection axis. The arrangement in a non-balcony or stadium house would require that the nominal throw be kept and that the projector be mounted on a retractable boom from the ceiling.
The characteristics of the modulation, or video amplifier, made it necessary to place this element adjacent to the kinescope. In past designs it had also been necessary to include the horizontal scanning wave amplifier near the kinescope deflection yoke, but this required more cabling to the projector and a great deal of physical space; therefore, a premise of the present design was to place all of the deflection equipment in the booth racks. The only electronic element of the equipment now remaining in the projector housing is the video power amplifier. The projector
consists then of the projection kinescope (the 7NP4) the optical elements, a 26in. mirror with a 22-in. correction lens together with the mounting or support of these elements. The electrical equipment is kept to a minimum with the required video amplifier, a blower for cooling the kinescope faceplate, and the necessary terminal boards to facilitate interconnecting wiring.
The equipment location can be seen in Fig. 3 which is a photograph of the projector with one-half the outer housing removed. The wiring is accessible by lifting the top protective cover which reveals the terminal board wiring side of the video amplifier. The amplifier is hinged to be tilted up and to the side, making the tube side of the chassis accessible and permitting adjustment or replacement of the kinescope. The projector is interlocked through the control panel to remove the high voltage if the cover is raised ; the interlock also actuates a shorting arm which contacts the
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March 1951 Journal of the SMPTE Vol. 56