| 摘要 |
PROBLEM TO BE SOLVED: To provide a finite system objective optical system which excels in workability of a lens, and has a small outside diameter and long entire length, whose spherical aberration, chromatic aberration and coma aberration are satisfactorily corrected, and which is suitable for in-vivo observation. SOLUTION: The finite system objective optical system 1 comprises, from an object side, a first group G<SB>1</SB>having positive power, a second group G<SB>2</SB>including a cemented lens, a third group G<SB>3</SB>comprising a biconvex lens L<SB>3</SB>, a fourth group G<SB>4</SB>including a cemented lens, and a fifth group G<SB>5</SB>having positive power, wherein cemented surfaces of the second group G<SB>2</SB>and the fourth group G<SB>4</SB>have negative refractive power. The objective optical system 1 satisfies following conditional expressions (1) to (7). The expression (1): 0.05<¾(1/F<SB>2</SB>+1/F<SB>5</SB>)/(1/F<SB>1</SB>+1/F<SB>3</SB>+1/F<SB>5</SB>)¾<0.25, the expression (2):ν<SB>2L</SB><75, the expression (3): 8<ν<SB>2L</SB>-ν<SB>2H</SB><30, the expression (4): 0.05<n<SB>2H</SB>-n<SB>2L</SB><0.15, the expression (5):ν<SB>4L</SB><75, the expression (6): 8<ν<SB>4L</SB>-ν<SB>4H</SB><30, and the expression (7): 0.05<n<SB>4H</SB>-n<SB>4L</SB><0.15. COPYRIGHT: (C)2009,JPO&INPIT
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