GB651035A - Improvements relating to optical apparatus - Google Patents

Abstract

651,035. Optical apparatus. DYSON, J., and ASSOCIATED ELECTRICAL INDUSTRIES, Ltd. July 19, 1948, No. 19337. [Class 97 (i)] To increase the working distance between an object and an objective especially for microscopic examination or optical projection an optical system is inserted therebetween comprising a concave reflector placed with its centre of curvature at or near the object and having a central aperture at or beyond which an image of the object is formed by light reflected by the mirror and by a substantially plane half-silvered reflector placed between the mirror and the object. In the microscope shown in Fig. 5, light from the object 5 passes through a cover glass 10 and a plate 4 having a semi-reflecting surface 3 to the concave mirror 1 whence it is reflected to the surface 3 and thence passes through the central aperture 2 of the mirror to form an image adjacent the microscope objective 9. Illumination is supplied by a lamp 12 and semi-reflector 11. The surface of the plate 4 facing the object may be convex to correct spherical aberration and a meniscus 15 concentric with the image of the centre of curvature of the mirror 1 formed by the lens 9 may also serve this purpose. Alternatively the plate 4 may be plane parallel and the illuminating beam be directed to the object by a prism carried by the face of the plate 4 facing the object. Only the peripheral areas of the plate 4 may be reflecting. In the form shown in Fig. 6 the concave mirror 19 and reflecting surface 21 are faces of a glass block 18 placed upon a glass plate 24 bearing a photographic emulsion 23 to be examined by a microscope objective 9, the system forming an image 20 of the emulsion at the aperture of the concave surface 19. All air spaces between the objective 9 and emulsion 23 may be oil filled. In a modification for observing objects in water the block 18 has secured thereto a glass plate having a central outer concave portion concentric with the surface 19, the block being placed in the water with the object at the common centre of curvature of the surfaces. The invention may also be applied to profile projection in which an objective forms a magnified image of the image formed by the concave reflector on a projection screen after reflection in a plane mirror.