Free-form optical surface measuring apparatus and method

摘要

Measuring apparatus for measuring a position of a device (2) that is rotatable relative to a movable stage (3), comprising: a measurement frame (4) and a contactless distance measurement device (5) for measuring in said first direction a distance between said measurement frame and a predetermined measurement surface (7) provided on said stage. According to the invention, said predetermined measurement surface is formed by a surface of said rotatable device. The method comprises providing a predetermined measurement surface on a rotatable device; and measuring directly on said rotatable device a first distance between a measurement frame and said predetermined measurement surface. In this way, aspheric or free-form surfaces of optical elements can be measured easily in closed loop without introducing abbe-errors.