GB863334A - Improvements in or relating to optical projectors - Google Patents

Abstract

863,334. Optical projectors. LEITZ G.m.b.H., E. Oct. 22, 1958 [Oct. 25, 1957], No. 33738/58. Class 97(1) An optical projector has sensing members which bear against the surface of an inserted transparency to sense the thickness thereof, and so arranged as to alter the gate-to-objective distance in accordance with the said thickness so as to maintain the transparency in the focal plane. The gate may be moved relative to the objective, or vice-versa. In Fig. 1 the sensing members are double-armed levers 6, mounted pair by pair on spindles 7, 7a attached to the transparency housing 4. The arms of the levers are of unequal length, the shorter arms 6a bearing against a surface 11 of the transparency gate 9; springs 12 are arranged between the housing 4 and surface 11. In the absence of a transparency, the supporting surface of the gate is in the focal plane. When a transparency is inserted, lever arm 6a is displaced by the amount of the thickness of the mount, but at the same time, the gate itself is displaced in the opposite direction, so that the transparency remains in the focal plane. The arms of lever 6 are unequal so as to take into account that the displacement must not only be half the thickness of the mount, but must also allow for apparent displacement of the focal plane due to refraction by the glass cover-plate. Fig. 2 shows a modified arrangement in which the objective, and not the gate, is displaced. A single-armed lever 13, pivoted at 15 to the housing 14, bears at its other end against the transparency 18. Part-way along the lever is a peg 19 which engages against a projecting part 20 of the objective 21. Thus the objective is moved in response to the sensed thickness of the transparency. In the arrangement of Fig. 5 (not shown) a "coarse" adjustment of the gate-to-objective distance is provided, in addition to the "fine" adjustment shown in Figs. i and 2. An electromechanical system for moving the transparency backwards and forwards is provided, which movement can be stopped by pressing a switch when the picture is in focus. A further arrangement for returning the transparency housing to a definite initial position is also provided.