Abstract: In a non-flexible endoscope consisting of an insertion section and an eyepiece section which are separable from each other, an optical system configured so as to correct chromatic aberration produced by an observation optical system disposed in the insertion section with an eyepiece optical system disposed in the eyepiece section. The optical system according to the present invention selects a simple composition for the observation optical system so that it is manufacturable at a low cost and disposable, and is configured so as to have favorable optical performance as a whole by correcting chromatic aberration produced by the observation optical system with the eyepiece optical system.

Abstract: An endoscope system having an endoscope, a scope holder holding the endoscope, a magnetic three-dimensional position sensor, and a TV monitor. The sensor detects the position of an object and generates data representing this position. According to the data, the view field of the endoscope is switched.

Abstract: A non-flexible endoscope comprises a slender insert section which is capable of being inserted from a leading end thereof into cavities of living bodies, an objective lens system for forming a primary image within the insert section, and a relay lens system for transmitting said primary image so as to form a secondary image, wherein the insert section satisfies the following condition:0.3<D.sub.1 /D.sub.2 <0.7wherein the reference symbol D.sub.1 represents a distance as measured from a first surface of the objective lens system to the primary image and the reference symbol D.sub.2 designates a distance as measure from the first surface of the objective lens system to the secondary image.