| 摘要 |
PROBLEM TO BE SOLVED: To provide an objective optical system having an adequate parallax and size of an image, without increasing the diameter of an endoscope in the measurement of a small diameter in particular and a stereoscopic endoscope. SOLUTION: This objective optical system has a pair of negative lens groups 1, a pair of positive lens groups 2, brightness diaphragms 3, second positive lens groups 4 and one image pickup element 8 arrayed successively from the object side. The second position lens groups 4 include a pair of positive lenses decentered more toward the respective optical axes on the object side than toward the brightness diaphragms 3.
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