Patent GB-899782-A (GB)
Title: Improvements in or relating to photographic cameras diaphragm aperture selecting devices
IPC: G03B7/12
Filed: 1960-10-03
Abstract: 899,782. Photographic cameras. BERTRAM, E., and BERTRAM, W. Oct. 3, 1960 [Oct. 2, 1959], No. 33816/60. Class 98(1). [Also in Group XL(b)] In a device of the kind which is attached to or incorporated in a photographic camera and preselects the camera diaphragm apertures prior to exposure, said device also being of the kind comprising a photo-electric cell, a movable shield, means for moving the movable shield to partially shield the photo-electric cell so as to take account of a predetermined exposure time or film sensitivity or of both exposure time and film sensitivity, a galvanometer which receives current from the photo-electric cell and preselects a diaphragm aperture according to the strength of current from the photo-electric cell and a sensing arrangement co-operating with the galvanometer and actuated at shutter release to set the diaphragm aperture to the preselected aperture, the galvanometer and the sensing arrangement are arranged in a first housing and the photo-electric cell is arranged in a second housing and the movable shield for partially shielding the photo-electric cell is moved by motion transmitted through a shieldcontrol lever arranged between the said first and second housings. In a first embodiment (Figs. 1 and 2) a camera diaphragm (not shown) is coupled by way of a gear-wheel 7 to a cylindrical exploring member 2 which-- on release of the shutter (not shown) for exposure-rotates in an anti-clockwise direction (Fig. 2) under loading of a helical spring 6 from a position in which a flap member 8 is held clear of the exposure meter pointer 4 by an abutment 10 on said exploring member through a position in which said flap member engages said pointer 4 to clamp it against transverse abutment rods 9 to a position in which one of the teeth of a stepped edge 3 engages with said pointer to stop the rotation of said exploring member 2 whereby the diaphragm is set to a value preselected by the exposure meter. The position of the pointer 4 coupled to galvanometer 1 is determined by the output of a photo-cell 22, the effective area of which is varied according to film sensitivity and shutter speed by means of a pivoted flap 20. This flap is coupled by way of a pinion 18 and rack 17 to a control lever 12 which is pivoted about a pin 13 and has a pin 14 engaging a semi-toothed cam disc 15 coupled to the film sensitivity and shutter speed setting rings of the shutter. A projection 4<SP>1</SP> of the pointer 4 projects into the path of a light beam directed by mirror 25 into the viewfinder field and co-operates with a translucent diaphragm scale 5 to indicate the stop value which will be set by the exploring member 2. Alternatively the scale may be carried by the projection 4<SP>1</SP> for co-operation with a fixed index mark. Additionally or alternatively, colours may be used to indicate when satisfactory exposure will result. In a second embodiment (Fig. 6) for cameras having a fixed shutter speed, the control lever 12 is coupled to a film sensitivity setting knob 33 by way of a lever 28 pivoted at 27 and having a pin 26 engaging with a cam surface 12<SP>1</SP>, and further by way of a slide member 29 having a bent-over slot engaging with said pin 26 and having a rack portion in engagement with a pinion 31 fast with said knob 33. In this embodiment the lever 12 directly engages the flap member 20, otherwise its functioning is similar to the first embodiment. In a third embodiment (Fig. 11) the film sensitivity setting knob 33 and the shutter speed setting member-not shown but coupled to a gearwheel 16-are coupled to the control lever 12 by way of a differential mechanism comprising a pinion 31 stiffly rotatable about a shaft 37, a gear-wheel 36 freely rotatable about the shaft 37 and coupled to gear-wheel 16 by way of a racked slide member 39, a gear-wheel 30<SP>1</SP> coupled to a control surface of the lever 12 by way of a racked slide 29<SP>1</SP>, and a planet wheel mounted on the wheel 30<SP>1</SP> and having two gear portions 34<SP>1</SP>, 35 engaging respectively with the gears 31 and 36.