観察光学系

Japanese Patent JP6666593

B2

PROBLEM TO BE SOLVED: To provide an observation optical system with an excellent optical performance, which has overcome problems such as dirt and scratches on the lens surface, including the degradation of contrast, while securing a moving space for a zoom moving group.SOLUTION: An observation optical system 10 has an objective system LO and an eyepiece system LE in this order from the object side. The objective system LO includes a first group Gr1 having positive power, a second group Gr2 having positive power, and a third group Gr3 having negative power, in this order from the object side. The objective system LO has an inverting optical system PR for erecting inverted images. The eyepiece system LE includes a fourth group Gr4 having positive power and a fifth group Gr5 having positive power, in this order from the object side. The third group Gr3 and the fourth group Gr4 move along an optical axis AX in a direction away from each other to change magnification from a low magnification to a high magnification, and also the following conditional expression is satisfied: 0.28