A turret condenser for microscopes comprising a turret, an aperture stop, a stop ring for opening and stopping down the aperture stop, a cam fixed to the turret, a lever means having one end in contact with the cam and the other end having a through hole formed therein, and a spring having one end fixed...http://www.google.ca/patents/US4368947?utm_source=gb-gplus-sharePatent US4368947 - Turret condenser for microscopes
