Patent GB-887907-A (GB)
Title: Photographic shutter
IPC: G03B9/10
Filed: 1960-10-10
Abstract: 887,907. Photographic shutters. AGFA A.G. Oct. 10, 1960 [Oct. 28, 1959], No. 34700/60. Class 98(1). A photographic shutter with at least one blade, the or each blade moving in one direction for one exposure and in the other direction for the next exposure and the or each blade having a driving spring with one end connected thereto, which spring is arranged to become partially re-tensioned during an exposure movement of the blade, has two pawis, each arranged to catch the moving blade in an opposite one of its directions of movement with the driving spring partially re-tensioned and to hold the stationary blade in one of its set positions. In a first embodiment (Fig. 2) having a single blade 4 of butterfly shape and pivotable about a pin 3, the blade 4 is normally caught and held after each exposure with one of its ends 4a or 4b covering the aperture 2 by one of the spring urged pawls 13, 14, engaging the pin 6, a blade driving spring 5 having one of its ends attached to the pin 6 and the other to a pin 8 on a lever 7 pivotable about pin 3 being partially retensioned during the final movement of the blade after exposure. The re-tensioning of the spring 5 is completed by rotating through one revolution a setting spindle 25 which carries a pinion 26 and through a crank arrangement 24, 22 pivots the lever 7 alternately into its two end positions. Release is effected by movement in the direction of arrow 36 of a spring urged lever 28 having a pin and slot coupling 31, 32 with a release member 33 which has a slot 34 engaged by a pin 35 on the lever 7 and is so positioned thereby as to actuate that pawl 13 or 14 which is holding the blade 4 in its tensioned position, the other pawl 14 or 13 being left ready to catch the blade after its ensuing exposure movement. For opening the blade, for example for focusing purposes in single lens reflex cameras, one end of a lever 40 pivotable about a pin 41 is depressed in the direction of the arrow 42 whereupon the other end of this-lever moves both pawls 13 and 14 simultaneously into their blade, releasing positions and the blade is therefore held in its open position (as shown) under the tension of its driving spring 5. The blade is returned to one of its closed positions by a spring urged lever 45 pivoted about pin 44 and having cam surfaces 49 and 50 for engaging the pin 6 when the abutment surface 46 is engaged by either of pins 47 or 48 on the crank wheel 24. In a second embodiment (Fig. 3) in which two blades 105, 106 are provided respectively pivotable about pins 103, 104. each having a driving spring 109, 110 and each being associated with a pair of spring urged locking pawls 111-114, each blade moves through 180 degrees at each exposure and functions alternately in successive exposures as the shutter opening blade and the shutter closing blade. For completing the retensioning of the driving springs there is provided an arrangement similar to that in the first embodiment and comprising a pivoted lever 115 to which one end of each driving spring is attached and which has a pin-andslot coupling with a crank wheel 118 coupled to a setting gear-wheel 120 and spindle 119. The locking pawls 111-114 are actuated for release of the shutter blades by lever arms 129-132 which rotate through 180 degrees about a shaft 125 under loading of a torsion spring 122-tensioned during setting of the driving springs by rotation of the crank wheel 118-when the pin 127 (or 126) on a gearwheel 124 has been released by a release lever 128. For varying the exposure time the lever arm pairs 130, 131 and 129, 132 may be relatively angularly adjusted, said first pair being mounted on an axle coaxial with shaft 125 and being positioned relative to the shaft 125 by the engagement of pins 134, 135 in any pair of a series of holes in said shaft 125. Means may be provided for maintaining the shutter open for focusing purposes in an analogous manner to that described for the first embodiment. Preferably, the pawls are of a synthetic plastic material and the driving springs have a core of resilient material to prevent oscillation thereof. The setting shafts 25 and 119 respectively may be coupled to an electric motor.