| 摘要 |
PROBLEM TO BE SOLVED: To obtain a vibration-proof optical system of an observation optical apparatus which is inexpensive, is small in size and is easily formable by forming a first lens as a vibration-proof lens which is driven in a direction orthogonal with the optical axis according to the vibration applied to the observation optical apparatus. SOLUTION: This optical system comprises, successively from an object side, an objective optical system I, an erecting optical system P and an eyepiece optical system II. The objective optical system I consists, successively from the object side, a first lens I-1 which has positive power and of which the one face is an aspherical surface, a positive second lens I-2 and a negative third lens I-3. The positive second lens I-2 and the negative third lens I-3 are cemented to each other. The eyepiece optical system II comprises, successively from the object side, a negative fourth lens II-4, a positive fifth lens II-5, a negative sixth lens II-6, a positive seventh lens II-7 and a positive eighth lens II-8. In such a case the second lens I-2 and the third lens I-3 may be in order of either of positive and negative or negative and positive. Vibration is prevented by driving the first lens I-1 in the direction orthogonal with the optical axis.
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