GB190405727A - Improvements in Optical Prisms and Instruments. - Google Patents

Abstract

5727. P³tz, P. F. March 8. Optical prisms.-Relates to prisms, and combinations of prisms, for use in telescopes, and other optical instruments. The elementary prism, out of which the varied combinations are formed, consists of a tetrahedron, Fig. 1, which may be looked upon as derived by the cutting of a cube in such a way as to obtain two of the four faces of the prism coincident with two adjacent ones of the cube, and in the for of right-angled isosceles triangles. These faces, e, f, form the inlet and outlet faces, while the others, c, d, totally reflect the light rays. The useless corners, a, b, may be cut away. Fig. 2 shows a pair of these prisms combined to act as a direct vision erecting- system. Fig. 7 shows a prism system for a binocular telescope each half of which consists of a pair of the prisms shown by Fig. 1. The light which enters the lower face of one half of the system from the objective is ultimately reflected at right-angles across to the second half, by which it is again reflected at right-angles, and into the eyepiece, with the result that the picture, presented to one eye, is produced by the objective opposite the other one. Fig. 8 shows a binocular fieldglass f fitted with the prism combination of Fig. 7. The body of the instrument is formed by tubes o, p, which telescope into one another to obtain an inter-ocular adjustment. A short intermediate tube t engages by an inclined slot u with a pin v carried by the outer tube o, which pin also projects into a slot 32 in the inner tube p. The rotation of the tube t, therefore, results in an alteration in the inter-ocular distance. The focussing-screw 8 acts upon the eyepieces. The prisms are secured in frames attached to the end covers C, D of the tubes o, p respectively.