US Patent 10036883 Endoscope magnification optical system and endoscope

An endoscope magnification optical system includes, in order starting from an object side, a first lens group having positive power, a second lens group having positive power, and a third lens group including at least a meniscus lens with a concave surface facing the object side and a positive lens, and the endoscope magnification optical system is configured to magnify an optical image by moving at least the second lens group in an optical axis direction with respect to the first lens group, which is a fixed lens group, while a distance from a lens surface located the closest to the object of the first lens group to an image plane is kept constant.