AUTOMATIC FOCUSING DEVICE PROVIDED WITH CORRECTION OF CHANGE IN FOCUS WITH TEMPERATURE IN CAMERA

摘要

PURPOSE:To enable correction of the rate at which a lens formed of a plastic is extended by changing the turning amt. of a distance ring in a camera having said lens by forming a stop lever into a bimetal construction so that said stop lever is deformed by following up to temp. CONSTITUTION:The image projected by a projecting lens 18 is reflected by an object and is detected by a photodetecting lens 19. Said image is formed on a photodetector 21, then the conduction of electricity to a coil 31b is interrupted by an arithmetic circuit to release the attractive holding of a stop lever 24 and an armature 30, thus allowing the lever 24 to be turned by the force of a spring 26. The pawl part 24a of the lever jumps into the required one of the pawl teeth 8d of a distance ring 8 to stop turning the ring 8. If a member 27 of a material having the larger coefft. of linear expansion than that of the lever 24 is preliminarily fixed to the lever 24, the lever 24 is deformed so as to incline rightward at a low temp. and an overhang D is obtd. in the part 24a on the outer side of the case in which the member is shrunk by the lever 24 alone. The turning amt. of the distance ring 8 is then made smaller than the turning amt. in the stage of an ordinary temp. when the lever is detained with the pawl tooth 8d of the ring 8 meeting a required object distance. As a result, the rate at which the lens is extended by an extending cam 8b is decreased and the focal position is correctly corrected.