Automatic focusing device for reflected light microscopes

An automatic focusing device for a reflected-light microscope having an optical system which may be switched between bright-field illumination and dark-field illumination, said microscope and focusing device comprising means for producing an illuminating light ray and for directing said light ray along an illuminating ray path toward an object to be observed, means for producing a ray of auxiliary illumination within a special wavelength region and for reflecting said ray of auxiliary illumination into and along said illuminating ray path to form with said illuminating light ray a combined beam, a stop (8, 28) cutting off a central part of said beam in said illuminating ray path when said microscope is switched to dark-field illumination position, said stop being a wavelength-selective filter which transmits in the wavelength region of said auxiliary illumination, and an incident-light reflector (9, 29) switchable between bright-field position and dark-field position and effective in said dark-field position to reflect a central part of said beam into a viewing ray path, said reflector when switched to said dark-field position being a dichromatic splitter mirror which reflects in the wavelength region of said auxiliary illumination and transmits in the wavelength region of the visible dark-field illumination.