Patent ID: 8767320

Claim:
An endoscope optical system, comprising: a front group; and a rear group, the front group and the rear group being arranged in this order from an object side such that an aperture stop is arranged between the front group and the rear group, wherein: the front group comprises a negative lens and a positive lens arranged in this order from the object side; the rear group comprises a positive lens and a cemented lens arranged in this order from the object side; and when f (unit: mm) denotes a focal length of an entire endoscope optical system, EX (unit: mm) denotes a distance (which takes a minus sign on the object side with respect to an image plane) from the image plane to an exit pupil, and f 2 (unit: mm) denotes a focal length of the rear group, the endoscope optical system satisfies conditions: −10< EX/f<− 6 (1), and 1.15< f 2 /f< 1.35 (2).