| 摘要 |
PROBLEM TO BE SOLVED: To highly precisely measure a clearance between a mask and a work. SOLUTION: A detection optical system is provided with the number of openings capable of setting a deviation d on an optical axis at the time of observing a real image (18) of a reference pattern formed on the mask (14) and a virtual image (18') of the reference pattern projected on the surface of a mirror-finished work (13) in a direction oblique to the mask (14) without focal depth. Then, an interval L between the real image (18) and the virtual image (18') on an image forming face (24) is measured, and a clearance between the mask (14) and the work (13) is converted from the interval L so that a clearance between the mask (14) and the work (13) can be adjusted.
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