Improvements in or relating to optical combining arrangements

899,234. Radio navigation. STANDARD TELEPHONES & CABLES Ltd. June 9, 1959, No. 19696/59. Class 40(7). [Also in Groups XIX and XX] In an arrangement for optically combining the indications of a plurality of indicators as images in one given plane, comprising a corresponding number of plane partially transparent mirrors arranged behind one another on an optical axis normal to the given plane, the reflection coefficients of successive mirrors are so graded that the brightness of each of the images is substantially the same proportion of the brightness of the corresponding indication. Cathode-ray tubes (C.R.T.s) 1..5 display aircraft bearings relative to ground D/F stations and transparent plate 6 bears a map 7 comprising transparent lines on an opaque background. Corresponding mirrors 11 . . 15 with reflection coefficients 1 /(r+ 1), where r is the number of the mirror from plate 6, are provided and the composite display is viewed through a telescope 16 or by a television camera, Fig. 2 (not shown). The mirrors may be films of transparent thermoplastic material stretched on frames and silvered on their front surfaces and with bloomed back surfaces. One C.R.T. may reproduce an adjustable marker and another may be a long-persistence tube reproducing a radar plan-position indication. In a modification the C.R.T. screen images are centred on corresponding circular scales which replace the map on plate 6. A further C.R.T. display may replace the plate; and the C.R.T. indicators may be replaced by illuminated pointer instruments.