Patent GB-191498-A (GB)
Title: Improvements connected with photographic cameras
IPC: G03B19/12
Filed: 1921-10-18
Abstract: 191,498. Loveless, W., and Atterton, W. Oct. 18, 1921. Cameras, reflex; shutters with pivoting blades.- Relates to shutter mechanism for reflex cameras, of the kind employing two co-pivotal shutter 'blades so constructed and arranged that (1) the shutter can be set to open the lens for focusing when the mirror is in lowered position in front of the film or plate, and to shut the lens before the mirror is lifted to disclose the film or plate, the opening of the lens for exposure not being effected until the mirror is fully raised to disclose the film or plate; and (2) the shutter can be set for time or automatic exposures, and consists in employing two spring-controlled blades of different width, the larger blade having an exposure slot, only partially covered by the smaller blade, which is provided with a setting handle. Stops are arranged on each blade so that on moving the smaller blade, it carries the larger blade with it to uncover the lens aperture for focusing, and the blades are then held. To make the exposure, the smaller blade is released, and moves to close the lens aperture, the mirror is raised automatically, and the smaller blade then carries the larger blade with it to open and close the lens aperture. Adjustable means are provided (1) to retard the movement of the blades for varying the time of exposure, and (2) to hold the shutter open for a time exposure. The shutter comprises (1) a sector-shaped blade 1 pivoted at 6 inside the rising lens front 7, and having an elongated exposure aperture 4, and (2) a narrower blade 2 mounted on the same pivot 6 and having an extension arm 2<a> projecting sideways from the rising front 7. The blades 1, 2 are normally re,- tained in the positions shown in Fig. 1 against a stop 30 by springs 12 and 12<a> respectively. Pins 8, 15, mounted respectively on the blades 1, 2 are adapted to engage catch points 22, 21 on an extension 20 of a lever 19 pivoted at 19<a> to the rising front 7, and the extension 20 carries a pin 23 slidably engaging a rod 24 mounted on levers 25, 25<a> turning respectively on a pin 25<b> fixed to the camera front 26, and a shaft 28 mounted .in bearings 29 on the camera body. The pin 25<b> and shaft 28 pass through slots 27, 27<a>, in the rising front 7 in order to permit this to be raised or lowered without interfering with the shutter mechanism. The shaft 28 carries an operating-lever 32 projecting outside the camera casing, and an arm 33 connected by a rod 34 to a bell-crank lever 35 which, when rotated by duepressing the lever 32, raises the mirror 36 from the focusing position shown in Fig. 5 into the exposure position against the ground glass screen 73. The shutter is set by depressing the arm 2<a> thereby rotating the blade 2. During this rotation, a projection on the blade 2 engages the pin 8 on the blade 1, and causes this to move with the blade 2 until the pins 8, 15 engage respectively above the catch points 22, 21. The lens aperture 3 is then uncovered through the lower portion of the aperture 4 for focusing. On depressing the lever 32 to make the exposure, (1) the lever 19 releases the pin 15 and allows the spring 12<a> to move the blade 2 in front of the lens aperture 3, where it is retained by the upturned edge 14 of the blade 1, which is still held by the catch point 22, (2) the linkage 33, 34, 35 raises the mirror into the exposure position, and (3) the lever 19 then releases the pin 8 and allows the spring 12 t:o move the blades 1, 2 together across the lens aperture, making the exposure and returning to the normal position shown in Fig. 1. On releasing the lever 32, the mirror 36 returns to the position shown in Fig. 5. For timed exposures, a dashpot is provided within the rising front, comprising a rod 41 connected to a piston in an air cylinder 43 haeving an 'air hole and carried by a strip 44 pivoted at 45 to the rising front 7. The rod 41 carries a pin 40 sliding in a slot in the strip 44, and engaging a keyhole slot 10 in a bent-over portion 9 of the shutter blade 1. The strip 44 may be rotated by turning an external pointer moving over an exposure scale in order to displace the pin 40 along the slot 10 towards or away from the pivot 6. When the shutter is released as described above to make the exposure, the action of the spring 12 is retarded by the dashpot to a greater or less extent according to the displacement of the pin 40 from the pivot 6. For time exposures, a catch is provided to retain the blades in the open position on depressing the lever 32 until this lever is released. This catch 56 is for:ned on a spring- controlled bell-crank lever 55 pivoted to a lever 54 which may be rotated, from the position shown in Fig. 1 for timed exposures, to an approximately horizontal position for time exposures, by turning a pointer co-operating with index marks on the outside of the rising front 7. When the lever 54 is so rotated, depression of the operating lever 32 causes the rod 24 to Engage a pin 58 on the bell-crank lever 55 and turn this so that the catch 56 lies in the return path of the pin 8 on the blade( 1. Thus, when the pin 8 is released from the catch 22, it is caught by the catch 56, and the blade 1 is retained in position uncovering the lens aperture 3 until the lever 32 is released and the pin 58 consequentially set free.