OBJECTIVE OPTICAL SYSTEM

摘要

PROBLEM TO BE SOLVED: To provide an objective optical system for sufficiently securing a space for arranging a spectroscopic element such as an etalon, a filter or the like and a driving system in an optical path, having long back focus, and applicable to an objective of an endoscope long in entire length. SOLUTION: The objective optical system comprises a first group G1 including two lenses L11 and L12 having negative refractive power and positive refractive power, a stop S and a second group G2 having positive refractive power in order from an object side, and satisfies a following conditional expression. 3.0