Abstract: A fiber bundle consists of first optical fibers and second optical fibers. At the distal end of the fiber bundle, the first and second optical fibers are bundled in a square close-packed array or a hexagonal close-packed array. The first and second optical fibers are separated from each other at the proximal end of the fiber bundle so that the first optical fibers are tied as a first branch bundle and that the second optical fibers are tied a second branch bundle.

Abstract: A zoom lens system includes a positive first lens group, and a negative second lens. Zooming is performed by varying the distance between the first lens group and the second lens group. The first lens group includes a negative first sub lens group and a positive second sub lens group.

Abstract: An adapter uses a monocular endoscope with a stereoscopic observing portion. The observing portion includes a system that divides light transmitted by the monocular endoscope into two light beams, and a pair of optical systems, each of the optical systems receiving one of the light beams and forming an image of the object. The images formed by each of the optical systems forming a stereoscopic image of the object, the adapter comprising a system that connects the observing portion to the monocular endoscope.

Abstract: A focusing method for a zoom lens system, including at least two lens groups, enables a portion of the zoom lens system to function as a focusing lens group over the entire focal length constituted by discrete focal length ranges. The portion of the zoom lens system, functioning as the focusing lens group, is changed to another portion thereof, in accordance with to the discrete focal length ranges.

Abstract: An illumination optical system includes a luminous body, and an illumination lens element through which light rays from said luminous body is diffused and emitted. The illumination lens element has peaks and troughs alternately provided on an incident surface or an exit surface thereof. A cross-sectional shape of the peaks and troughs is a curved surface defined by a periodic function which can be differentiated, or the peaks and troughs are formed by a plurality of straight lines approximating the curved surface.

Abstract: An objective lens for an endoscope includes a front lens of negative power, an aperture stop, and a rear lens group of positive power in this order from the object side. At least one surface of the front lens group and/or the rear lens group is a compound aspherical lens made of a glass lens and a transparent layer applied to the glass lens surface. A surface of the transparent layer farther from the glass lens is an aspherical surface. The refractive index n of the glass lens to which the transparent layer is applied is more than 1.65 (n>1.65).