Positioning mechanism for positioning auxiliary optical device relative to main optical device and the auxiliary optical device

摘要

A positioning mechanism for positioning an auxiliary optical device relative to a main optical device, and the auxiliary optical device. Thje positioning mechanism includes a positioning member and a positioning recess which are provided on one and the other of the main and auxiliary optical devices, respectively so as to be engaged with each other with a clearance. Each of the positioning member and the positioning recess includes a leding side face portion and a trailing side face portion being opposite to and in alignment with the leading side face portion in a direction of relative movement of the main and auxiliary optical devices. The trailing side face portions of the positioning member and the positioning recess have a configuration which allows the trailing side face portions not to contact with each other when the relative movement is effected at a speed faster than a predetermined speed.