Abstract: A method and a device for making the distance between a human eye and an eye-examining instrument coincide with a preset distance. A miniature light source disposed on the image end of an objective lens of the instrument illuminates the eye. The light specularly reflected by the surface of a cornea is converged. The miniature light source is positioned to have the converging point lie on the surface of an image of the fundus formed by the objective lens. Accordingly if the distance between the human eye and the instrument coincides with a preset distance, the image of the light source on the image surface of the objective lens becomes sharp. An operator looking into a view finder correctly adjusts the position of the instrument by moving the latter until the image of the light source becomes sharp.

Abstract: An ophthalmoscopic photographing and observing system eliminates rays of light reflected and scattered at the cornea and the crystalline lens of a human eye. An illuminating optical system is provided with light shielding stops at positions conjugate to the corneal surface, the iris, and the rear face of the crystalline lens of an eye being examined. The sizes of these light shielding stops are such that an image of the stop conjugate to the corneal surface covers an area on the cornea where the light reflected by the fundus of the eye passes through the cornea covered with an image of the stop which is conjugate to the corneal surface; an image of the stop which is conjugate to the rear surface of the crystalline lens covers an area on the rear face of the crystalline lens where the light reflected by the fundus of the eye passes through. A ring-shaped aperture stop is conjugate to the iris.

Abstract: An opthalmoscopic optical system for photographing the fundus of an eye by an ophthalmoscopic camera, it is necessary to illuminate the ocular fundus through the cornea. On the cornea, however, a part of the illuminating light is reflected with the result of production of halo in an image of the ocular fundus. This can be avoided by separating an illuminating light incident area of the cornea from that serving for the emergence of image forming rays to keep this part free from reflexes. According to the present invention, there is positioned between an objective lens and an image-forming lens aligned on a common optical axis is an inclined illuminating plate is positioned between objective lens and an image-forming lens of such construction that a mirrored central area in the vicinity of the optical axis is surrounded by an annular transparent zone which directs light from an illuminating arrangement to the objective lens to suppress the production of a halo.

Abstract: The present invention relates to an eye fundus camera free from undesired reflected and diffused light beams. The camera uses a photographic optical system including an objective lens, a reflecting means, an aperture means, a photographic lens system for imaging the eye fundus to be inspected in sequence on a photographic plane and an illumination optical system including at least a light source, a relay lens and a ring-shaped aperture. The optical system leads the light beam from the light source to the eye to be inspected through the reflecting means and the objective lens, whereby the ring-shaped aperture is positioned in the illumination optical system in such a manner that the image of the ring-shaped aperture is formed near the iris in the eye to be inspected while the aperture is positioned in such a manner that the conjugate position of the aperture with reference to the objective lens is near the cornea to the eye to be inspected.

Abstract: The present invention relates to an eye bottom camera which is so designed that in order to eliminate the undesired light beam reflected by the objective lens opposed to the eye to be inspected the objective lens as one group of biconvex type whereby by making the undesired light beams reflected on both surface of the objective lens as if they were produced by a light beam emitted from a same plane of the illumination optical system the small black spot provided on the same plane can be made small and further by so designing that the image formed in the neighborhood of the objective lens, of the small black spot appears at the position closer to the eye to be inspected than the surface of the objective lens it is made difficult that the small black spot be formed on the eye bottom to be inspected.

Abstract: The present invention relates to an optical instrument for examining the eye fundus which is so designed that in the optical system including an objective lens visible, targets are built for orientating the visual line of the eye to be inspected along the direction convenient for the inspection of the desired part of the eye fundus in order to be able to inspect the desired part. The visible targets are located at the position conjugate to the eye fundus with regard to the optical system including the objective lens in order that the light beam coming from the targets through the objective lens reaches the eye to be inspected. The image of the visible targets is formed on the eye fundus of the eye to be inspected while the eye to be inspected observes the visible targets through the objective lens in such a manner that the visual line is oriented in the direction along which the targets are seen.

Abstract: Described are insulated gate-type field effect transistors used in capacitive memory circuits and having protective diodes for protecting the insulating films below the gate electrodes from electrical breakdown, in which parasitic transistor action which might be caused by minority carriers injected into semiconductor substrates by noise signals applied to the protective diodes are eliminated by means for suppressing injection of minority carriers or by means for preventing injected minority carriers from reaching the drain regions of the field effect transistors.

Abstract: The present invention relates to an improvement of the alignment system for the pupil in an eye-fundus camera. An auxiliary lens is provided so as to be freely inserted and pulled out at an optical path behind an object lens in an optical system for observing and photographing an eye fundus wherein said auxiliary lens is inserted at the same position as that of an image of the eye fundus which is formed by said object lens when said auxiliary lens is not inserted. Thus the image of a pupil is formed so that observation of the pupil becomes possible by an eye-fundus observation finder and the alignment of the pupil becomes easy.

Abstract: Insulated gate-type field effect transistors used in capacitive memory circuits and having protective diodes for protecting the insulating films below the gate electrodes from electrical breakdown, in which parasitic transistor action which might be caused by minority carriers injected into semiconductor substrates by noise signals applied to the protective diodes are eliminated by means for suppressing the injection of minority carriers or by means for preventing injected minority carriers from reaching the drain regions of the field effect transistors.