Patent ID: 7142284

Claim:
A position detector for detecting a relative positional relationship between an original form that has a position detecting mark, and a stage that supports the original form and has a reference mark, said position detector comprising: an illumination optical system for illuminating the position detecting mark or the reference mark using illumination light; a detection optical system for introducing reflection light that is reflected from the position detecting mark or the reference mark, to an image pickup unit; and a controller for varying at least one of a numerical aperture of the detection optical system, a numerical aperture of the illumination optical system and a wavelength of the illumination light to control contrast of a mark signal that is detected by the image pickup unit and indicates the position detecting mark or the reference mark, wherein said relative positional relationship is detected using offsets generated in a predetermined numerical aperture of the detection optical system, a predetermined numerical aperture of the illumination optical system and a predetermined wavelength of the illumination light measured beforehand.