| 摘要 |
The invention relates to a high-performance imaging optical system that achieves a magnification high enough to be capable of microscopic viewing under an endoscope, and is compatible with high-definition imaging devices. The objective optical system comprises, at least in order from the object side, a positive, first group G1, a second group G2 and a third group G3. In association with an object point change, at least the second group G2 is moved along an optical axis. The objective optical system satisfies a condition with respect to an optical magnification &bgr; upon focusing on the closest range.
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