AUTOMATIC FOCUSING DEVICE FOR OPTICAL SYSTEM EXPANDING OBSERBATION APPARATUS

摘要

PURPOSE:To fix the strength of light reflected by a sample surface and to improve automatic focusing accuracy by subtracting the value corresponding to other reflected light converted from a laser output from an output of a photoelectric element which receives reflected light by the sample surface and other surfaces. CONSTITUTION:Reflected light by a polaroid beam splitter 43 of light 23 projected from a semiconductor laser generator 20 is detected by the 3rd photoelectric element 50. The 2nd photoelectric element 41 detects a part 46 of light reflected by an objective lens and a part 47 of light reflected by a sample and a detection output Va from the 3rd element 50 to which the sum of outputs Vb and Vc from the 2nd element are outputted is converted into Vd through an amplifier 51. An output Vc from a differential amplifier 52 controls the generator 20. Thus, the generator is controlled so that the strength of the reflected light 45 from the sample surface is fixed. Therefore, focusing is precisely detected by a pinhole 32 and a photoelectric element 33 even at the movement of the sample.