| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide an imaging optical system for endoscope which can switch a wide angle observation state and a telephoto observation state and can satisfactorily correct aberration. <P>SOLUTION: The imaging optical system for endoscope comprises: a first negative group; a second negative group; an aperture diaphragm; a third positive group; and a fourth positive group in this order from an object side. The first group is constituted of a lens turning its concave surface on an image side. The second group is constituted of a cemented lens including a negative lens and a positive lens turning their concave surfaces to the object side in this order from the object side. The third group is constituted of a cemented lens including a negative lens and a positive lens in this order from the object side. The fourth group includes at least one cemented lens, switches from a wide angle observation state to a telephoto observation state by moving the third group in the direction of approaching the aperture diaphragm along an optical axis, and satisfies the following conditional expression: ν<SB POS="POST">n3</SB><ν<SB POS="POST">p3</SB>. In the expression, ν<SB POS="POST">n3</SB>is the Abbe number of the negative lens of the cemented lens of the third group, and ν<SB POS="POST">p3</SB>is the Abbe number of the positive lens of the cemented lens of the third group. <P>COPYRIGHT: (C)2012,JPO&INPIT |
