Microscope transmitting light illumination system using the kohler system

Claim 1

A microscope having a frame and a specimen stage and including a rotatable nosepiece and an eyepiece mounted relative to said stage in optical alignment along a viewing axis, said nosepiece including a plurality of objective lenses having different illumination requirements and being selectively positionable on said viewing axis, said microscope being characterized by the following improvement: an illumination system including, in optical alignment along an illumination axis, a light source, a condenser, and a variable focal length lens system between said light source and said condenser, said variable focal length lens system having a lens element moveable along said illumination axis, said lens element being connected to a motor for translation in either direction along said illumination axis, said motor being responsive to a control signal, a reference signal generator including a plurality of reflective surfaces, each of said reflective surfaces being associated with and adapted to identify a separate one of said plurality of objective lenses by reflecting only a predetermined portion of an incident beam of light so as to provide a coded reflected beam, a signal light source positioned to illuminate one of said reflective surfaces when the corresponding objective lens is on said viewing axis, a detector positioned to receive and respond to illumination reflected from the reflective surface, said detector generating a reference signal having a characteristic peculiar to the particular objective lens in said viewing axis, a potentiometer for generating a position signal having a contact mounted on said lens element thereby providing a characteristic signal peculiar to the actual position of the lens element, a controller connected to said reference signal generator and potentiometer, said controller comparing the peculiar characteristics of the reference signal and the position signal and providing a control signal to said motor when the peculiar characteristics differ so as to move said lens element until a null is attained whereby a predetermined position of said lens element is reached to provide the proper illumination for the selected objective lens.