US Patent 10898061 Endoscope magnification optical system, endoscope, and endoscope system

An endoscope magnification optical system includes, in order from an object side, a first lens group having a negative power, a second lens group having a positive power, and a third lens group having a meniscus lens with a convex surface facing the object side. A distance from a lens surface of the first lens group that is nearest to the object side to an image surface is kept constant while the second lens group is moved in an optical axis direction with respect to the first lens group and the third lens group, which are fixed lens groups, and thereby an optical image is magnified.