| 摘要 |
972, 857. Photographic shutters. AGFA A.G. April 11, 1961 [April 14, 1960], No. 13059/61. Heading G2A. In a shutter having a retarding mechanism including a pivoted lever arranged to act on a shutter driving member and pivotable to a variable extent into the path of the driving member during the running down of the shutter, the pivoted lever is arranged to transmit movement from the driving member to a pivoted balance mass so that, starting from the position of the lever for the slowest shutter speed setting in which it extends furthest into the path of the driving member; displacement of the lever out of said path causes the mechanical advantage between the lever and the balance mass to be progressively increased, whereby the resistance to movement of the lever is decreased. Preferably the arrangement is such that the mechanical advantage increases uniformly with the displacement of the lever and the shutter retarding mechanism is constructed so that, for equal successive movements of the shutter timing cam which may be continuous or have steps of approximately equal magnitude and controls the retarding mechanism, the corresponding shutter speeds selected are in geometrical progression. As shown, the invention is applied to a multiple pivoted blade shutter having a blade ring 3 driven through a triangular cam from a spring- powered master member 25 which is cocked and released as described in Specification 921,286, the nose 5 of a pivoted retard lever 6 engaging a control edge 4 of the master member and the tail 9 engaging a rotatable balance disc or flywheel 12, and the setting of the lever being controlled by a pin 15 on it engaging the stepped shutter speed setting cam 16. Thus as the shutter runs down the point of engagement between the lever and the balance mass moves so that its distance from the lever pivot 7 remains approximately constant while its distance from the flywheel pivot 13 increases. Instead of a sliding engagement between the flywheel and lever a pin and slot connection may be provided, and the master member may engage a pin on the retard lever. For adjustment in manufacture to obtain the desired retardation effect, the pivots 7, 13 of the retard lever and the flywheel and the pin 15 and if desired the pin engaged by the master member may be eccentrically mounted. If desired the flywheel may co-operate with a second retard device which can be put out of action by means of a second shutter speed setting control cam. Such an arrangement is described (Fig. 2 not shown) applied to a setting type shutter having separate spring-driven concentric blade rings as described in Specification 964,199, a second flywheel having a radial face engaging a pin on the flywheel engaging the retard lever. As alternatives, the second retard device may comprise an escapement wheel which may be concentric with, or formed on, the flywheel.
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