Patent GB-698001-A (GB)
Title: Improvements in or relating to photographic cameras
IPC: G03B7/04
Filed: 1951-05-22
Abstract: 698,001. Photographic reflex cameras provided with photo-electric exposure meters. ZEISS IKON AKT.-GES. May 22, 1951 [May 22, 1950], No. 11981/51. Class 98 (i). [Also in Group XL (b)] A reflex camera including a photo-electric exposure meter has a setting member which on the one hand controls the position of a movable abutment, the camera lens diaphragm being normally open but arranged to close whenever an exposure is made to a working setting determined by the position of the said abutment, and on the other hand is coupled with an adjusting means by which the overall sensitivity of the exposure meter may be varied so that such sensitivity is simultaneously set whenever the aperture to be employed is preselected. As shown, the diaphragm adjusting ring 1 of the objective 2 of a reflex camera is geared to a housing 3 for a spring 4, to a gear 5 loosely mounted on the shaft of a gear 6 'connected to both the reflex mirror and a film winding and shutter setting device (not shown), and to a gear 10. A differential gear 26 controlled by shutter speed and film speed adjusting discs 29, 33 rotates bodily, through a worm 25 and worm wheel 24, a meter 23 electrically connected to a photo-cell 21 provided with a diaphragm, the pointer of the meter being visible in the field of the camera focusing screen 35 which carries a reference mark 36. The photo-cell diaphragm is controlled by a ring 19 geared to a manuallyoperable adjusting wheel 16 which meshes also with gear 12 loosely mounted on the shaft of the gear 10. After an exposure, the film is wound on, the reflex mirror is returned to the viewing position, and the shutter is set, all by means not shown which also rotates the gearwheel 6 anticlockwise. A dog 7 thereon thus engages a dog 8 on the gear 5 and rotates it clockwise to open fully the diaphragm for the objective, and simultaneously to tension the spring, the said spring being prevented from closing the diaphragm due to the gear 5 being locked by the winding means. At the end of the winding, the pin 9 abuts against an arm of a pivoted pawl 15 to free a ratchet wheel 14 fixed to the gear 12. Next, by rotating the wheel 16, the desired aperture is set to a value indicated by the scale carried by the photo-cell diaphragm, and the film speed is set by means of the disc 33. The shutter speed disc is then adjusted, and through worm gearing 27, 28 and differential gear 26 rotates the meter bodily to register its pointer with the mark 36. The selecting of the aperture by wheel 16 rotates also the gear 12 so that for apertures other than the largest the dog 13 on the gear 12 is moved away clockwise from the dog 11 on the gear 10. On pressing the shutter release, the coupling between the gear 6 and the winding means is released so that the spring 4 rotates the gears in the directions shown by the arrows and closes down the objective diaphragm until the dogs 11, 13 engage, the pin 9 on the gear 6, which is rotated by the gear 5 by means of the dogs 7, 8 releasing the pawl 15 to lock the ratchet wheel 14 at the start of this movement to hold the gear 12 and hence the dog 13 stationary. Thereafter the reflex mirror is raised and the shutter released to make an exposure. If desired when preparing for an exposure, the shutter speed may be selected before the aperture, the meter pointer then being brought back to the mark 36 by rotating the wheel 16. Instead of employing a diaphragm to adjust the photo-cell current in accordance with the aperture selected for the exposure, an adjustable resistance controlled by the wheel 16 may be included in the photo-cell circuit.