US Patent 7573629 Blade actuating apparatus for optical instruments

A base plate is provided with four guide pins and a rotor has four output pins so that each of four blades is provided with a plurality of slots. Individual slots provided to the blades are selectively fitted to the four guide pins and the four output pins so that when the rotor is reciprocated and rotated, the blades are capable of continuously changing the size of an aperture by cooperation of their aperture forming edges while maintaining a regular octagon.