Apparatus for measuring the dimensions of a minute object

Abstract

An optical apparatus for precisely measuring the dimensions of an object comprises an objective lens for forming an enlarged image of the object, a screen member onto which the enlarged image by the objective lens is projected and which is movable in a direction parallel to one direction on the image plane of the enlarged image, the screen member including a slit formed perpendicularly to the one direction, and a reflecting surface which is provided in an area including the surroundings of the slit and onto which the enlarged image is projected, observation optical means for observing therethrough the enlarged image on the reflecting surface, the observation optical means having a relay lens, and a field lens provided in opposed relationship with the reflecting surface of the screen member, the imaging light beam of the object from the objective lens passing through the field lens onto the reflecting surface of the screen member, the imaging light beam of the object reflected by the reflecting surface of the screen member passing through the field lens into the relay lens, the field lens having an optic axis that is in a plane perpendicular to the reflecting surface of the screen member and parallel to the slit and that is inclined with respect to the normal to the reflecting surface.