Patent GB-990388-A (GB)
Title: Diaphragm control arrangement
IPC: G03B7/085
Filed: 1962-02-13
Abstract: 990,388. Automatic control of light; photographic cameras; cine cameras. K. VOCKENHUBER, and C. HAUSER. Feb. 13, 1962 [Feb. 17, 1961],No.5456/62. Headings G2A,G2E and G3R. In a diaphragm control arrangement for a camera, a galvanometer, without restraining force, controls the movement of at least one blade of a diaphragm and a photo-resistor is arranged behind the diaphragm to be in the path of rays coming through the main objective of the camera, or in the path of rays through a special objective having a diaphragm moved in correspondence with the diaphragm of the main objective. The coil of the galvanometer has two axial windings one of which is energized through the photo-resistor and the other through a comparison resistor. As shown, in a camera having an objective lens 1, and a variable magnification objective system 2, 3, 4 a portion of the light to the objective is reflected by a prism 8 to a view-finding comprising lens 7, a prism 8a and an eyepiece 9. A shutter 11 is rotatable about a shaft 12 by a motor 16 through gearing 15 to interrupt the light path between the objective and a film 10 which is intermittently fed by a claw 19 operated by a cam 18. The shutter 11 is mirror-coated on the side facing the objective so as to reflect the incident light through a lens 13 to a photo-resistor 14. A neutral filter 25 is interposed between the lens 13 and the photo-resistor when the shutter is not rotating and is swung out of the light path when a release button 22 is depressed to move a lever 21. The filter compensates for the mirror-surface reflecting light on to the photo-resistor for only a fraction of a revolution. The button 22 shifts the lever 21 from a locking disc 20 and closes contacts 23 to energize the motor from a source 24 through a main switch 32. Diaphragm blades 37, 38 are connected to galvanometer rotors 35, 36. Each galvanometer rotor is positioned by the opposing torques due to the magneto-motive forces in a pair of coaxial windings, one of which is energized from a source 24 through a photo-resistor 14 and the other through a comparison resistor 31, the coil positioning the diaphragm so that the light incident on the photo-resistor is maintained constant, a graded neutral filter 26 is rotatable in front of the photo-resistor 14 to adjust for various film speeds. Alternatively, the photo-resistor is not operated at one point on its characteristic and the adjustment for film speed, or frame frequency, is effected by a logarithmic resistor, Fig. 3 not shown. In modifications, the opening and closing of the diaphragm is controlled at rates determined by capacitors and the control circuit is energized from an alternator driven by the shutter motor. It is stated that the photo-resistor can be replaced by a photo-diode or a photo-transistor and that mirror 11 can be replaced by a partiallysilvered mirror or a prism. It is also stated that a special objective with a diaphragm, driven in common with the diaphragm of the camera objective, can be positioned in front of the photoresistor. The special objective diaphragm can be formed by prolongations on the camera diaphragm.