GB135223A - - Google Patents

Abstract

135,223. Barr & Stroud, Barr, A., and Stroud, W. Oct. 30, 1916. Range-finders.-In single-observer range-finders comprising a double telescope supported within a comparatively long outer tube carrying doubly reflecting prisms or mirrors at each end, an extra telescope for coincidence instruments, and one or two extra telescopes for stereoscopic instruments, are provided so as to present to the observer one or more large fields of view surrounding or adjacent to the small fields of view presented by the double telescope. Fig. 8 shows, in plan, a coincidence range-finder having a third objective 20 the rays from which are deflected upwardly and then horizontally by a prism system 22 to a prism 23 by which they are deflected downwardly into the eyepiece prism system. Various eyepiece prisms systems may be employed. In the system shown in Fig. 4, which is applicable to the construction of range-finder shown in Fig. 8, the central ray from the right-hand end of the instrument is reflected by the hypotenuse of the prism 8 on to the face 15; it then strikes the silvered upper half of the hypotenuse of the prism 13 and is reflected through the prisms 5, 6 to the eyepiece 3. The central ray from the left-hand end is reflected by the hypotenuse of the prism 9 through the lower half of the prism 13 to the eyepiece. This system may be modified by the substitution of a rhomboidal prism for the prisms 5 and 13. Fig. 2 shows an eyepiece prism system similar to that shown in Fig. 21<b> of Specification 1462/03. The central ray R from the right-hand end of the instrument is deflected downwardly by a double reflecting-prism before entering the prism 8, and it is then reflected as indicated to the upper face of a biprism 5. The central ray L from the left-hand end enters the prism 9 and is reflected as indicated to the lower face of the biprism 5. In the system shown in Fig. 3, the rays entering the prisms 8, 9 are reflected by the surfaces 12, 10 respectively through the prisms 5, 6. In each of these systems, the rays from the extra telescope pass normally through the face 7 into the prism 6 and are reflected by its hypotenuse so as to present a field of view surrounding the small fields, the image being formed in the plane of the separating-line 1. In stereoscopic range-finders, an extra telescope may be provided for one or each eye, and the. eyepiece prism systems may be suitably modified.