| 摘要 |
PROBLEM TO BE SOLVED: To observe wide visual field at low magnification with sufficient brightness and to easily operate a sample in an observation method for observing a dark image such as fluorescent observation by satisfying a specified condition in an objective lens constituted of four groups. SOLUTION: This objective lens is composed of a 1st group G1 consisting of a biconvex lens, a 2nd group G2 consisting of a meniscus combined lens obtained by sticking a positive meniscus lens and a negative meniscus lens, a 3rd group G3 consisting of a biconcave lens, and a 4th group G4 consisting of a meniscus combined lens obtained by sticking a negative lens and a positive lens and a biconvex lens. The lens satisfies the conditions NA/β>=0.055, WD/FL>=0.18, 1.6>=FL/L>=1.2, FL>=80 and 90>L>=5O. NA is the numerical aperture of the objective lens,βis the magnification of the objective lens, WD is the actuation distance of the objective lens, FL is the focal distance of the objective lens and L is a distance from a microscope attaching surface to an observation surface.
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