Abstract: A microscope optical system for observation of test object, comprises an objective lens and a compensator provided to be inserted into and retracted from the optical path of the objective lens. The compensator is inserted into the optical path according to the change of the optical path length of the medium between the object lens and object to maintain good image forming performance irrespective of such change of the optical path length.

Abstract: Disclosed is a horizontal position detecting device for maintaining the surface of a body to be inspected vertically to the optical axis of a main objective lens. The device includes an illumination optical system and a condenser lens system. The illumination optical system supplies parallel light rays to the surface of the body from the direction oblique to the optical axis of the objective lens. The condenser lens system condenses the light rays supplied by the illumination optical system and reflected by the surface of the body. The optical axes of the illumination optical system and the condenser lens system are arranged substantially symmetrically with respect to the axis of the objective lens.

Abstract: A projection type exposure device includes a main projection objective lens for projecting onto a wafer a predetermined pattern on a negative plate to be projected, a main illuminating optical system including a condenser lens for illuminating the negative plate to be projected, and an alignment optical system for forming the image of a reference mark provided on the negative plate to be projected and the image of an alignment mark on the wafer through the main projection objective lens from between the condenser lens and the main projection objective lens. The alignment optical system has a first objective lens and a second objective lens for condensing the light beam from the first objective lens, the first and second objective lenses being disposed on the same optical axis, and a reflecting member for bending the optical axis so that it is orthogonal to the negative plate to be projected. The first objective lens and the reflecting member are movable together relative to the negative plate to be projected.