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Parallax (perspective error) allows us to process the world in it's true three dimensional state, closer objects appear relatively larger than those placed farther away. This phenomenon of changing magnification as a function of working distance is found in most conventional imaging systems, however it is unacceptable in some metrology applications where the part under inspection is of finite depth that is greater than the depth of focus of the lens system. Telecentric lenses optically correct for this occurrence so that objects remain the same size independent of their distance, over a range defined by the lens. A telecentric lens system typically incorporates an afocal design with the aperture stops located at the common focus of the front and back lenses, resulting in the chief rays being parallel to the optical axis in both the object and image spaces. A constant viewing angle and a constant magnification can therefore be achieved in the case when: The object and image surfaces are tilted with respect to the optical axis The lens is defocused on either object surface or image surface