| 摘要 |
PURPOSE:To accurately detect the position of a surface to be detected in which an objective lens has a low magnification but the reflectivity distribution is not uniform by providing an auxiliary optical system and varying the magnification of a pattern image to be imaged on a detected. CONSTITUTION:A luminous flux L1 of an infrared light of a light source 1 after passing an opening 3a is condensed to a board surface 7a through an objective lens 6. A reflected luminous flux L2 of the surface 7a is reflected on mirrors 9, 5 and arrives at the photoreceiving surface of a photoelectric detector 8. Here, the image of the opening 3a is focused at a center on the photoreceiving surface when the surface 7a is disposed on an article of the lens 6, and a defocused image is formed on a left (right) side region of the photoreceiving surface when the surface 7a is disposed blow (above) the surface of the article. A focus detector 22 detects the position of the surface 7a from the photoelectric conversion signal of the light to be output from the detector 8. In this case, when the lens 6 of the low magnification is replaced so as to alter an observing magnification, its imaging magnification is lowered. Thus, an enlarging optical system 10 is disposed in an optical path between the mirror 5 and the detector 8 to increase an imaging magnification, and out of focus due to the influence of the pattern on the surface 7a is prevented. |
