International projectionist (Oct 1931-Sept 1933)

Record Details:

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March 1932 INTERNATIONAL PROJECTIONIST 15 simultaneously with the tilting already mentioned, from position 1' to 3', and leaves the beam as soon as it reaches position 3'. Continuing, a second mirror commences the same route through the beam into position 1' and terminates, similar to its predecessor, in position 3'. Thus the movement of the second film picture is cancelled, and the third mirror enters the beam. In this manner eight sectoral plane parallel mirrors revolve about the spindle h, and a suitable gearing of the mirror turning device and the film conveyance ensures exact synchronization of film transport and compensating device. As the mirrors succeed one another without break, parts of two sector mirrors are simultaneously present in the beam for a minute space of time during each change of film picture. Compensating Action While one mirror is still compensating for the movement of a certain film picture, the next mirror has already begun to do the same with the following picture, so that in each change of pictures the reproductions of two successive pictures are transposed on top of each other on the screen. In the^ same measure now [as during the movement of the pictures, the receding mirror is caught by a gradually decreasing part of the beam, and the following mirror receives a proportionally increasing part of the light beam], the clearness of both transposed reproductions on the screen gradually changes, but leaves the actual clearness unchanged. Thus, without dark intervals, one screen view will always fade into the following, without enabling the Fig. 3. — Mirror mech'inism as seen from front and reverse eye to detect any change-over at all. The reason for this is that the movement of the tape, i.e., the change of pictures, is faster than can be followed by the eye. Only at speeds of less than 8 to 10 pictures per second is the changing of one picture into the next one visible. To avoid losing the extra light gained by the dropping of the shutter, through simultaneously projecting several film pictures, the projection beam in the film track must be moved in synchronism with the movement of the film tape. Therefore, a highly illuminated, square front window is projected on to the individual film pictures through a special objective, and the light beam projected on to the same mirrors before the film that effect the optical compensation behind it. Thus the sector mirrors are made use of twice, and produce vibrations in the beam also before the film, that cause the reproduction of the front window to advance with the individual pictures to a certain distance in the film track, then disappearing downward, to reappear above subsequently. For the practical employment of the apparatus in scientific institutes it is of greatest importance that the clearness of reproduction remain constant, as it is thus possible to reduce the operating speed down to about 2 or 3 pictures per second; at this frequency, the individual pictures are clearly distinguishable, and enable an exact observation of even the slightest degree of development. The full construction of the apparatus ready for use is shown in Fig. 4. The mirror arrangement is enclosed, oilproof and dustproof, in the inclined drum. Fig. 3 shows the front of the opened mirror casing, from which all sector mirrors except one have been removed to convey a better idea of the construction. The tilting movements of the individual mirrors causing the optical compensation are effected by the sliding of guide pins in a link of a special curved shape. Recent Improvements The latest Mechau model (Fig. 3), is remarkable for its particularly high degree of accuracy, and has been greatly improved and its efficiency increased to meet modern requirements in every way. Because of the uninterrupted, not jerky, film conveyance the machine runs almost noiselessly at any speed, and vibrations are entirely avoided. The constant and ■J 1 j i K li mm j^^HBv ^^vW 1 ac,^ IH| ■yr\ 1 ' ■ j^SSf^Su^^KL. iBn 11 a^CHbIRi S Fig. 4. — Full vieiv of projector showing friction gear Fig. 5. — Projector with opened film guide and (at left) sound ray appliance