Abstract: An illumination optical system for use in an endoscope comprises a glass pane disposed in front of a source of illuminating light and which is centrally defined with a reflecting surface which is inclined with respect to the optical axis of the source. Light passing through the source in alignment with the optical axis thereof illuminates a near object while light passing through the source offset from its optical axis illuminates a far object.

Abstract: An objective lens system for endoscopes comprising a first lens group having positive refractive power, a second lens group having negative refractive power and a third lens group having positive refractive power, and being so adapted as to permit focusing and at the same time observation at a magnification level different from ordinary magnification level matched with distance to an object to be observed.

Abstract: An optical system for connecting a first light guide to a second light guide in such a manner that the rays emerging from said first light guide are incident on said second light guide. Said optical system is so adapted as to assure favorable angular distribution characteristic and plane luminous intensity distribution by arranging the emerging end surface of said first light guide in the vicinity of the front focal point of said optical system and the end surface of incidence of said second light guide in the vicinity of the rear focal point of said optical system respectively.

Abstract: A photo eyepiece for endoscopes comprising at least two cemented lens components, i.e., a first cemented lens component and a second cemented lens component, having a large numerical aperture and, in spite of this merit, corrected very favorably in characteristics of spherical aberration, lateral chromatic aberration and curvature of field.

Abstract: A method for focusing an objective lens of endoscope comprising dividing said objective lens into a front lens group and a rear lens group, arranging an optical fiber bundle so as to have its end surface on the rear side of said rear lens group and focusing said objective lens by displacing said rear lens group together with said optical fiber bundle. This method makes it possible to afford high magnification level for the objective lens even when it is brought into focus with an object located at a short distance.