| 摘要 |
PROBLEM TO BE SOLVED: To clearly visually recognize an index line formed on an index plate in an observation device like a telescope. SOLUTION: An index plate 10 is arranged on an optical axis of an eyepiece optical system 20. The index plate 10 has a glass plate 11 and a glass plate 12. One face 11a of the glass plate 11 and one face 12a of the glass plate 12 are joined. Cross lines are formed on the face 11a of the glass plate 11 by chrome evaporation or the like. A radius of curvature of the face 11a is made substantially equal to the curvature of field of a sagittal image surface of the eyepiece optical system 20. COPYRIGHT: (C)2004,JPO
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