Ocular zoom optical system and optical instrument

摘要

Provided are an ocular zoom optical system which has a wide apparent field of view even on a low power side and in which aberrations are favorably corrected while a sufficient eye relief is secured over the entire zoom range, and an optical instrument including the ocular zoom optical system. The ocular zoom optical system 3 includes, in order from the object side: a first lens group G1 having a negative refractive power; a second lens group G2 having a positive refractive power; and a third lens group G3 having a positive refractive power and at least one aspheric surface. An intermediate image I′ is formed between the first lens group G1 and the second lens group G2. During zooming, the third lens group G3 is fixed on the optical axis, and the first lens group G1 and the second lens group G2 are moved in directions opposite to each other with the intermediate image I′ interposed therebetween. The second lens group G2 includes, in order from the object side: a positive single lens L21 having a higher positive refractive power on the lens surface on the eye-point side than that on the lens surface on the object side; and a positive cemented lens CL2 including a positive lens L22 and a negative lens L23.

主权项

1. An ocular zoom optical system, comprising, in order from an object side: a first lens group having a negative refractive power; a second lens group having a positive refractive power; and a third lens group having a positive refractive power and at least one aspheric surface,
wherein an intermediate image is formed between the first lens group and the second lens group, during zooming, the third lens group is fixed on an optical axis, and the first lens group and the second lens group are moved in directions opposite to each other with the intermediate image interposed therebetween, the second lens group comprises, in order from the object side: a positive single lens whose lens surface on an eye-point side has a higher positive refractive power than a lens surface on the object side has; and a positive cemented lens comprising a positive lens and a negative lens, and conditions of following expressions are satisfied,
2.155,f2/(fC2−fF2)>90,where a focal length of the second lens group is f2, a focal length of the single lens is f21, an Abbe number of a medium of the single lens is νd21, a focal length of the second lens group for C-line is fC2, and a focal length for F-line is fF2.