Patent ID: 6456384
Filing Date: 2002-09-24
Classification: G01B

Abstract:
An apparatus for measuring flatness of a test surface using moirÃ© topography comprising:an illuminating system including a light source and an optical pathway for conveying light from the light source to the test surface; an imaging system including a fringe pattern detector and an optical pathway for conveying an image of the test surface to the fringe pattern detector; a grating pattern that is illuminated on the test surface by the illuminating system and that is imaged onto the detector by the imaging system for producing together with a reference grating pattern a moirÃ© fringe pattern indicate of the flatness of the test surface; a focusing optic positioned at an intersection of the optical pathways that convey light both to and from the test surface en route from the light source to the detector; the focusing optic being arranged as a part of the illuminating system and as a part of the illuminating system to collimate light en route to the test surface at a first angle thereby contributing to forming on the test surface a telecentric reproduction of the grating pattern; and the focusing optic being arranged as a part of the imaging system and as a part of the imaging system to relay collimated light at a different angle from the test surface thereby contributing to forming on the detector a telecentric image of the grating pattern reproduction appearing on the test surface.