Abstract: An illumination optical system for endoscopes wherein, in order to make it possible to make an illumination of a uniform and sufficient brightness over a wide range of the surface of an object to be observed, a cover lens arranged in front of the exit end face of a light guide is so formed that its surface on the object side may be a convex aspherical surface or may be a convex spherical surface or may have a concave center part and larger in the refractive index in the peripheral part than in the center part. The light guide may be a light emitting device.

Abstract: In order to enable an easy acquisition of a bright excellent differential image and an excellent ordinary image of an object requiring observation, the photoelectric microscope using a position sensitive device in accordance with the present invention comprises: a laser light source; an objective lens for collecting, onto the object requiring observation, a laser light emitting from the light source; a beam splitter disposed between the light source and the objective lens; a position sensitive device receiving the laser light emitting from the light source and having transmitted through the object requiring observation; and a position sensitive device receiving, through the beam splitter, the laser light reflected from the object requiring observation. To allow two-dimensional scanning, a pair of opposing galvanometric mirrors may be disposed at a pupil position between the beam splitter and the objective lens.