| 摘要 |
PROBLEM TO BE SOLVED: To obtain an objective lens having high transmissivity and with little self-fluorescence by satisfying specified conditions in the objective lens constituted of three lens groups. SOLUTION: This lens is constituted of a 1st lens group G1 being positive, a 2nd lens group G2 being positive and a 3rd lens group G3 being negative. The 1st lens group G1 includes three consecutive positive lenses, that is, a plano-convex signal lens L1, a single lens L2 and a single lens L3 which have positive refractive power and are made of quartz glass and whose surfaces on an object side are plane in this order from the object side. The conditions 0.8<f1/F<3, n2<1.64, n3<1.64, 60<ν2 and 60<ν3 are satisfied. F is the focal distance of the entire objective lens and f1 is the focal distance of the lens L1. Then, n2 andν2 respectively mean the refractive index and the Abbe number of the lens L2 with respect to a d-line. Besides, n3 andν3 mean the refractive index and the Abbe number of the lens L3 with respect to the d-line. Thus, the high transmissivity is obtained for stimulating light whose wavelength is to 340 nm.
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