| 摘要 |
PROBLEM TO BE SOLVED: To easily carry out maintenance for constituent components of a beam-focusing part, such a lens system. SOLUTION: Respective constituent units 22, 23 of a beam focusing part 20 are fixed in a body by elastic force of springs 61, 71 generated by the engagement of the upper ends of the springs 61, 71 with hooks 60, 70. When maintenance of the constituent units 22, 23 is carried out, the engagement of the springs 61, 71 with the hooks 60, 70 is released and the constituent units 22, 23 are extracted from an opening U formed in the upper face of the body 2.
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