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940 HANDBOOK OF PROJECTION FOR
THE MIRROR.— In order that the light from the back side of the filament be not wasted, and that the light source present to the lens a solid unbroken surface, a spherical mirror is employed placed as per Figs. 365 and 366. The reasons for this mirror, and an explanation of its action will be found in the text matter, page 817.
It is of course vitally important that the mirror be so placed that the image it reflects or projects will fall exactly in its appointed place, and the Simplex equipment provides ample adjustments, in convenient form, to enable the projectionist to place the image exactly where he wants it.
CLEANLINESS.— It is essential to efficient results that the mirror be kept perfectly clean. You must polish its surface daily. This may be done by washing it with a solution of half wood alcohol and half water, or with gasoline, polishing the surface while still wet. It may also be done by breathing on surface while mirror is still cold and polishing with a perfectly clean, soft cloth, or with tissue paper.
We would recommend to theatre managers that they provide, for the purpose of cleaning lenses, a roll of soft high grade toilet paper. Such paper is most excellent for the purpose, and clean lenses mean much in excellence of screen results.
To remove or insert a mirror it is only necessary to loosen thumb screws XXX, Figure 366, and insert or take out the mirror, as the case may be.
CAUTION. — After inserting a mirror be sure to tighten thumb screws XXX, but only sufficiently to hold the mirror in position, without exerting undue pressure. DON'T jam the thumb screws down tight, unless you want a broken mirror.
DISTANCE. FILAMENT TO MIRROR.— Distance center of back of mirror from lamp filament must be as shown in optical diagram, Fig. 359. This is important to good results. The correct distance may be obtained by turning knob A, Fig. 366 in the required direction.
Having placed the mirror in position and secured the correct distance back of mirror to lamp filament, unlock the mirror by turning knob D, Fig. 366, to the left, and swing the mirror to one side as far as it will go by means of knob C. Fig. 366 locking it there by means of knob D. This is to prevent focusing the filament image, which is not desired at this stage of the proceedings.