The present invention relates to an improved shutter dial locking device which functions to block the rotation of a shutter dial and to hold the same in a preset position corresponding to a particular mode of operation.
A conventional photographic camera commonly has a shutter dial which is rotatable for presetting the shutter speed within a range of from 1 second to 1/1000 second and at the same time for selecting the mode of operation among automatic electric exposure control, manual exposure control, X-contact synchronization control and mechanical exposure control wherein the shutter is mechanically operated at a predetermined speed when the electric control fails.
However, if a shutter dial which has been preset to a position of a desired mode of operation is subsequently accidentally or inadvertently moved to a different position, the shutter is operated in a different control mode in the actual photographing operation, giving undesired photographic results. This situation can occur no matter in what position the shutter dial is preset, that is to say, in any one of the positions of the automatic electronic exposure control, the manual exposure control and the mechanical exposure control. As the shutter is controlled in a completely different manner in each one of these operation modes, it is desirable to provide means for holding the shutter in the preset position once it is set in one of these positions.
In FIGS. 8A and 8B of the drawings there is illustrated a conventional stop or lock mechanism which is designed to block the inadvertent shift of the shutter dial, wherein a hollow shutter dial shaft 17 is provided with a release member 18 slideably, longitudinally movable within the hollow space of the shutter dial shaft 17 and with a spring member 19 for biasing the release member to project outwardly beyond the surface of the shutter dial plate. The release member 17 is provided at one end with a stop member 20 for engagement with a longitudinal groove which is formed in the inner wall surface of the shutter dial shaft 17. On the other hand, a number of stepped portions are formed on the inner periphery of the shutter dial shaft bearing, except for those surface portions facing the longitudinal groove. The stop of the releasing member 18 is held in engagement with the longitudinal groove to prevent rotary displacement of the shutter dial only when the dial is preset in the automatic exposure control position. With the known shutter dial stop construction described above, however, in order to release the stop device, it is necessary to finger depress the release member at the center of the shutter dial to lower the stop to the stepped portion. The release member 18 has to be maintained in the depressed state while the shutter dial is rotated into a different position with the other fingers of the hand. This operation is often found difficult and troublesome since the shutter dial, per se, is very small. As the dial setting accordingly requires a two-stepped operation, that is to say, the depression of the releasing member and the rotation of the shutter dial, it is not practical if used in photographing operations which require prompt action. Furthermore, from a structural point of view, it is disadvantageous to provide a stop and a spring within a hollow space of the shutter shaft which is only several millimeters in diameter in view of the difficulties which will be encountered during the manufacturing and machining processes of the shafts. In addition, the blocking of the shutter dial movement has been possible only in the automatic exposure control as the stopper member is designed to engage a longitudinal groove on the shutter dial shaft.