| 摘要 |
PROBLEM TO BE SOLVED: To provide a bitelecentric objective lens by which various kinds of aberration and the telecentricity of the main light beam of an off-axis luminous flux are sufficiently corrected. SOLUTION: This lens consists of a front group and a rear group having positive refracting power as a whole. The front group consists of a first group G1 formed of a cemented lens of a convex lens and a concave lens and a second group G2 formed of a convex lens or a cemented lens of a convex lens and a concave lens and a concave lens. The rear group consists of a third group G3 formed of a concave lens and a cemented lens of a convex lens and a concave lens and a fourth group G4 formed of a cemented lens of a convex lens and a concave lens. The optical constant of each lens is set so as to satisfy the expressions of (1) n1n -n1p >0.1, (2)ν1p -ν1n >25, (3) 0.3fF<|r2n|<0.5fF, (4) 1.4<(r2p /r2n )<2.7, (5) n3n <n3p .
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