GB633140A - Improvements relating to photographic reflex cameras - Google Patents

Abstract

633,140. Photographic reflex cameras with exposure meters. SOC. CIVILE MOROY. April 9, 1947, Nos. 9414 and 9415. Convention dates, April 19, 1946, and March 7, 1947. [Classes 97 (i) and 98 (i)] [Also in Group XL (b)] A photographic reflex camera of the kind having a photo-electric cell on the mirror so that when the measurement of the time of exposure is made the cell is located in the direct path of the light rays issuing from the objective lens, and a micro-ammeter measuring the current generated by the cell, has an indicator movable along the path of the microammeter needle by means which also displace the shutter speed control, so that alignment of the indicator with the needle sets the shutter speed required for the amount of light falling on the cell. As shown, Fig. 4, the objective 1 is mounted on a rising and falling front. The mirror 3 is slidable on an insulating support 4 pivoted horizontally at 6, and spring-urged so that its front edge slides on the camera wall during part of its travel. It has a thin coating 3a of photo-electric material, e.g. caesium, connected by leads 8, 9 to a microammeter 10 on top of the camera. Light admitted by the objective falls on the layer 3a to generate a current, and is reflected to form an image on a ground glass screen 14 covered by a removable or collapsable hood 15 with an eye. piece 16. A pointer 30, Fig. 2, has an internally toothed sector 20 engaging a pinion 21 rotatable by a disc 23. Pinion 21 is geared to the shutter speed control so that when pointer 30 is aligned with the needle 17 of the micro-ammeter 10, the shutter speed is adjusted. for the correct exposure. Pointer 30 is pivoted at 19 to a plate 31 slidable to disengage pinion 21 from sector 20 for adjustment for emulsion speed by means of a pointer 32 and a scale on disc 33. Ths shutter is of known kind, e.g. a sliding-plate shutter wherein the interval between the release of the plates is determined by an airbrake adjusted by a cam. In a modification, an aluminium surface layer of the mirror transmits about 25 per cent of the incident light to a pure iron plate coated with selenium beneath the mirror. The iron plate and a peripheral copper strip in contact with the selenium are connected to the micro-ammeter on the side wall, the needle of which moves in a vertical plane, and has a bent-over end moving above the viewing screen. A similar needle on the other side of the camera is brought into alignment with the first by a knob geared to the shutter speed control. The needles and a co-operating scale on the top of the camera are self-luminous. A variable resistance housed in the control knob may be connected in series with the meter and cell and adjusted according to the speed of the emulsion by a scale with separate indications for daylight and artificial light.