| 摘要 |
PROBLEM TO BE SOLVED: To provide a practical real image type observation optical system keeping an image magnification and a field rate though its entire length is shortened. SOLUTION: The real image type observation optical system is constituted of an objective optical system 10 having positive refractive power as a whole, an inverting optical system 20 positioned near the image-formation surface of the optical system 10 and having a plurality of reflection surfaces, a field frame 30 arranged between a plurality of reflection surfaces, and an eyepiece optical system 50 having positive refractive power as a whole in order from an object side to a pupil side, and satisfies a following conditional expression. (1): 0.01<S<SB>1</SB>/fe<SB>1</SB><SP>2</SP><0.15, provided that S<SB>1</SB>means the area of the aperture part of the field frame 30 and fe<SB>1</SB>means the synthetic focal distance of a 2nd inverting prism 20b being a part of the optical system 20 and the optical system 50 positioned nearer to the pupil side than the field frame 30 in the expression. COPYRIGHT: (C)2005,JPO&NCIPI |
