| 摘要 |
PROBLEM TO BE SOLVED: To obtain an objective lens having longer operating distance in comparison with a conventional objective lens and large numerical aperture capable of making the light beam of a near ultraviolet range to standard wavelength by composing a third group lens of plural single lenses and arranging at least plural achromatic combined surfaces in a second group lens. SOLUTION: The third group lens is composed of three or more single lenses and at least two or more achromatic combined surfaces are arranged in the second group lens. when the whole length of a lens system is defined as OAL, the focal distance of the third group lens is defined as (f III), the radius of the curvature of the first surface of a first group lens by counting it from an object point side is defined as Rf, that of the final surface of the first group lens is defined as R'f, that of the first surface of the third group lens by counting it from the object point side is defined as Rr, that of the final surface of the third group lens is defined as R'r and the synthetic thickness of the first group lens is defined asΣdf, the condition of an expression is satisfied by the objective lens having the long working distance. This objective lens having the long operating distance can be used as the high-magnification objective lens for a high-temperature microscope excellent in resolution impossible heretofore.
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