Patent GB-993433-A (GB)
Abstract: 993,433. Reflex cameras. VOIGTLANDER A.G. Jan.26, 1962 [Jan.30, 1961], No. 3099/62. Heading G2A. In a single lens reflex camera having a normally fully open diaphragm and a photoelectric exposure meter, the light-sensitive cell of which can be brought mechanically into the path of rays from the camera objective, a single movement of a separate manual device is adapted to bring the exposure meter cell into the ray path and to bring the diaphragm under the control of a pre-selector mechanism. The diaphragm pre-selector may be separately actuated before during or after movement of the manual device. Preferably the manual device operates so that the diaphragm is set in accordance with the pre-selector before the meter cell is brought into the operative position to avoid incorrect exposure measurements. The shutter release mechanism which also moves away the reflex mirror is connected with the actuating mechanism of the diaphragm so that prior to the start of the exposure the diaphragm is set to the value pre-selected and used in the light-measurement operation. As shown, on depression of the button 8 on a pivoted lever 10, pin 13 idles along the slot 15 in the pivoted segment lever 16 while pin 14 moves clockwise the pivoted lever 29 to effect via link 36 and stud 57 anticlockwise pivoting of the lever 9 about its cam follower end 42 to move the rod 47 downwardly to engage the plunger 51 which operates the adjusting arm of the diaphragm 65. The setting of the cam 6 on the diaphragm aperture pre-selecting ring 5 determines the initial position of the rod 47 and hence the distance through which the plunger 51 is driven by the rod 47 to close the diaphragm 65 from the fully open position. When the pin 14 passes the elbow 60 its further movement does not alter the position of the lever 29 since the pin merely slides along the surface 61 but pin 13 now drives the lever 16 and gear segment 18 anticlockwise so that via arm 21 a slide 25 bearing an exposure meter comprising a photoconductive cell 27 and a measuring instrument 26 is moved over the camera viewing and focusing screen 64. The cell is connected as one arm of a Wheatstone bridge, with a variable resistor 71 in the other arm across the battery and with measuring instrument 26 between the junction of these arms and a tap 68 on a voltage divider resistor 69 forming the ratio arms. The diaphragm having been preselected, the bridge is balanced by adjusting the tap 68 which is secured to the shutter speed (or film sensitivity) setting ring 81. Alternatively the shutter speed may be preselected and on pressing the button 8 the bridge may be balanced by adjusting the diaphragm preselector ring 5. In an alternative arrangement, the measuring instrument 26 may be replaced by a polarized relay which drives a motor controlling the setting of the unselected variable either shutter speed or diaphragm preselector value in accordance with the light value measured. Instead of null point operation the measuring instrument may be provided with a scale of shutter speeds and the ring 81 adjusted to produce the desired indication on the scale, the cell response being varied in accordance with the shutter speed chosen either by a variable resistor or by a mask adjustable in front of the cell. Exposure is effected by operating a shutter release button 7 (Fig. 1 not shown), which release causes before exposure raising of the mirror and a plunger 40 to depress the adjustable end 39 of the lever 38 so that the diaphragm is set in accordance with the preselected value, without affecting the linkage 29, 36.