GB130048A - Improvements in or relating to Optical Instruments. - Google Patents

Abstract

130,048. Vickers, Ltd., and Burns, W. A. Jan. 4, 1918. Optical systems for sighting-de vices,. eyepieces, micrometer, crosswire, and like.-Optical instruments are provided with separate graticules for night and day use respectively, the former being of the " transparent " type and appearing superimposed upon the latter, is of the solid" type, when illuminated. In the construction sbown in Fig. 1, a glass cube formed from two prisms W<1>,W<2>is placed with the front. face, on which is formed the day graticule G<1>, in the focal plane of the telescope objective O. The night graticule G<2> is formed on the top of the cube and is covered by a disk D of opal glass &c., which diffuses the illuminating-light. The prisms are cemented together with an optical cement of nearly, but not quite, the same refractive index as the glass, so that the surface of junction transmits most of the light but serves also as a partial reflector to produce an image of the night graticule, For convenience in adjusting, the night graticule may be formed on the underside of the disk D. In the construction shown in Fig. 3, the use of cement is avoided, the plain glass meeting being inclined at 55 degrees to the optical axis. and the plane of the night graticule G<2> correspondingly inclined. The day sight C<1> may be of a different pattern from the night sight G<2>, as shown in Fig. 4. A " skeleton " construction avoiding the use of solid glass masses, shown in Fig. 6, comprises a glass sheet M acting as a reflector for the night graticule G<2> formed on a disk of glass, the night graticule G<1> being also on a disk of glass. The duplication of reflected images produced bv the sheet M may be utilized to produce the effect of a single line crossed by two parallel lines ; or it may be avoided, as shown in Fig. 7, by forming the sheet M as a weak prism, a correcting-prism M<1> being inserted, or the diaphragm carrying the day graticule G<1> being prismatic. In an eyepiece, Fig. 8, having an inverting prism P<1>, the reflecting-surface required to bring the night graticule into the field of view may be the face f<3>, an auxiliary prism p<2> being used to receive rays from the illuminated graticule G<2> and reflect, them to the face f<3>; in a modification, the mark 0<1> is used to provide the required by a double reflection and a refraction; in another modification, the image of a mask o obtained by reflexion from the prism face f<1> is reflected back again by the plane surface of the field lens F bearing the day graticule G<1>.