GB891348A - Improvements in and relating to optical comparators - Google Patents

Abstract

891,348. Optical compositions; projection systems. WATSON, MANASTY & CO. Ltd. July 13, 1960 [Aug. 7, 1959], No. 27146/59. Class 97(1). In order to compare opposite surfaces of an object, separate images thereof are projected in superposed or closely adjacent relationship, by an optical system including means whereby the images are presented in the correct relative "hand" for direct comparison. As shown in Fig. 1, light from opposite sides of an object 1 is directed through lenses 4, 5 so as to be combined at semi-reflecting surface 8 into a single beam and thus form superposed images on a screen. In the light path of one beam to the surface 8 there is disposed a prism 12 which serves to reverse the image carried by this beam, without inverting it, lenses 4, 5 may be omitted, a single lens being disposed after the surface 8. Parallelism of the beams entering lenses 4, 5 may be ensured by use of a mirror 2 and an optical square 16, 17, as shown in Fig. 3, in which the. beam combining surface is a half-silvered glass sheet 15 and difference of optical path is compensated by a glass sheet 18. Two pairs of superposed images, differently magnified, if desired, may be formed by an arrangement as is Fig. 4 wherein beams from opposite sides of object 1 are combined at a semi-reflector 19 and the two image pairs are respectively formed on screens 21 and 48. In this case, the semi-reflector 19 may be replaced by a prism which is hexagonal or wedge-shaped so that light entering through one face emerges after reflection at a semitransparent surface in a direction perpendicular to another prism face (Figs. 13, 14 not shown). A coloured light source or filter may be arranged in one or each light path to facilitate image comparison. The object 1 may be opaque or transparent. Various other optical arrangements are described.