| 摘要 |
PROBLEM TO BE SOLVED: To obtain an optical length measuring device capable of measuring with high accuracy of 1μm or less. SOLUTION: A projection optical system TO and an observation optical system KA are arranged to face on the same light axes Z1 to Z2 (light axis) by way of a member to be measured (work) 10, a specific projection image is projected on the work 10 wall surface and relatively move on the light axis and the wall surface of the work 10, an X-indication part 14 for obtaining the measured value S of an inter-wall distance D is obtained from the moving quantity S' and indicated, an optical system is arranged as focus position disagreement of the first focus position P1 of the projection optical system TO and the second focus position P2 of the observation optical system KA. Three dimensional correction part 20 operating for correction of three dimensional curved surface correction value 23 in accordance with the three dimensional error of the optical system concerning the X-indication part 14 and a measured value S and outputting the measured results are provided. The optical length measuring system is capable of measuring the inner diameter of the circular wall surface with high accuracy by constituting to indicate the measured results in the X indication part 14 by the output.
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