Automatic focussing appts. for surgical microscope - obtains coincidence of modulated IR beams by adjusting objective lens via servomotor

摘要

The device has the operating field illuminated by two modulated IR beams (12,12b) which converge with one another within the focal plane of the collimating lens (1) forming the objective. When the microscope is correctly focussed the two beams (12,12b) alternatively line up with the same circular zone of the focal plane tthe centre of which is the focus of the objective. The objective is automatically adjusted by a servomotor receiving signals from photodiodes each receiving light from one of the reflected beams (12,12b). Pref. each viewing path has a Lummer cube which splits the light from the operating field into two parts respectively directed to one of the eyepieces and the corresponding photodiodes.