Abstract: An objective optical system for an endoscope comprises a retrofocus objective lens assembly consisting of a front-stage diverging lens unit, an aperture diaphragm, a rear-stage converging lens unit, and a prism positioned in this sequence, and a self-scanning solid state image pickup device positioned at the image formation surface of said objective lens assembly. The objective lens assembly satisfies the conditions 0.8<.vertline.f1.vertline./f.ltoreq.1.5, 1<f2/f.ltoreq.1.5, and Np>1.7, where f denotes the resultant focal length of the whole assembly, f1 denotes the resultant focal length of the front-stage diverging lens unit, f2 designates the resultant focal length of the rear-stage converging lens unit, and Np designates the refractive index of the prism.

Abstract: A holographic endoscope transmits light to an object and receives and transmits the image of that object. The light transmitted is used to illuminate an object with one of two beams which are derived from a single laser, while the image received is transmitted from the object. The light from the image transmitted passes through a field lens, and a second beam or reference beam is made to interfere with this light. The resulting interference pattern is recorded on a photographic plate, forming the hologram.

Abstract: A variable focal length lens adapter is attached to an endoscope at its eyepiece. The lens adapter includes a lens system constituting a variable focal length lens system in combination with the eyepiece. The lens system of the lens adapter is composed of a negative lens group located next to the eyepiece, a positive lens group located next to the negative lens group and a second negative lens group located next to the positive lens group on the side opposite to the first negative lens group. The first negative lens group and the positive lens group are axially movable to vary the focal length of the total lens system of the adapter. The last negative lens is used as a diopter adjusting lens.

Abstract: An imaging system for use in an endoscope includes a vari-focal lens system provided in a viewing head to be inserted into a cavity or opening of a living body or machinery, a solid-state image sensor for imaging an image formed by the lens system to produce electrical signals representative of the image, a supporting unit for supporting the lens system and the image sensor thereon so as to change the spacing between the lens system and the image sensor on the optical axis of the lens system, and controller circuitry operable in response to magnification of the lens system for estimating the position of a focus of the lens system to control the supporting unit so as to position the image sensor substantially at the estimated position of the focus.

Abstract: A wide angle objective is located at the entrance face of a flexible image guide tube of an endoscope and a variable focal length eyepiece lens system is located at the exit face of the tube. The variable focal length eyepiece lens system includes an axially movable lens group which increases the magnification of the endoscope from the normal 20 times to about 40 times, in effect, increasing the magnification 20 times over the magnification potential of current endoscopes.