PHOTO-ELECTRON TYPE FOCUSING ERROR DETECTOR

摘要

An opto-electronic focussing-error detection system is described for detecting a deviation between a radiation-reflecting surface and a plane of focussing of an objective system in an optical imaging system. The detection system comprises a beam-splitting element and a radiation-sensitive detection system arranged behind the beam-splitting element and two groups of detectors. The first group is associated with a first sub-beam and the second group with a second sub-beam of two sub-beams formed by the beam-splitting element. The beam-splitting element is a compound wedge comprising two wedge sections having a common base surface and each having an upper surface situated opposite the base surface. The upper surfaces are inclined relative to each other in the plane of the interface between the two wedge sections with that plane extending substantially perpendicularly to the base surface and to the upper surfaces and containing the optical axis of the imaging system. The two groups of detectors are each situated one side of a plane containing the optical axis and extend substantially perpendicularly to the interface.