Abstract

In a photographic shutter, an opening blade and a closing blade are settable in respective tensioned positions from which the blades can be released to first uncover and then recover an exposure opening. A cam device is mounted for unidirectional rotation to release the blades from their tensioned positions and to reset the blades to such positions. The cam device has an arcuate camming surface which extends spirally about the axis of the cam device from an area of minimum radius to an area of maximum radius as the cam device is rotated. A step-like surface of the cam device connects the areas of maximum and minimum radii to cause an abrupt drop from the maximum radius area to the minimum radius area. Respective springs urge the opening and closing blades against the camming surface. This causes each blade to be released from its tensioned position to drop from the maximum radius area to the minimum radius area when the maximum radius area moves out of the way of the blade, and causes each blade to be reset to its tensioned position when the maximum radius area moves back to the blade.