| 摘要 |
PURPOSE:To exactly detect an image position by a plane-shape sensor which can easily be manufactured, by reflecting a beam from an object, which has passed through an observation lens, by a conical surface mirror, and detecting the image position by the plane-shaped sensor being vertical to an optical axis of a lens. CONSTITUTION:An image of a mark T which has been formed on an object O by irradiating an optical beam B is reflected by a cylindrical mirror, M, reflected by a conical mirror MC after passing through an observation lens L, and projected onto a plane-shaped image position detecting sensor P being vertical to an optical axis of the lens L. By detecting a position in the radial direction on the sensor P of the mark image, a distance extending from the lens L to the object is measured, and it becomes the same as a fact that the sensor P is positioned on an optimum image pickup surface PF. Since the mark T is shaped like a point, the mark image on the sensor does not become blurred irrespective of a distance to the object. Accordingly, an image position is exactly detected by the plane-shaped sensor P which is easily manufactured. |
