GB674193A - Improvements in or relating to optical comparators - Google Patents

Abstract

674,193. Optical comparators. EASTMAN KODAK CO. Dec. 8, 1949 [Dec. 9, 1948; Dec. 9, 1948; Dec. 9, 1948], Nos. 31529/49, 31530/49 and 31631/49. Class 97 (i). In an optical comparator, a magnified image of an illuminated work-piece positioned on a work-holder is projected on to a viewing screen by an optical system comprising a first objective system for receiving light from the work-piece and for forming an aerial image thereof, and a second objective system optically aligned to receive light from the aerial image and to project a magnified image thereof on to the screen. As shown in Fig. 2, the comparator includes a work-holder 15 which is movable along and perpendicular to the optical axis and which carries a work-piece 14 illuminated by a lamp 11, the light from which is collimated by condenser 13. Light from the work-piece passes through an afocal system consisting of lenses 16, 17 which may be of equal focal length and are separated by the sum of their focal lengths.. The light is then directed vertically by a pentareflector 20 and an aerial image 21 of the workpiece is formed in the plane of a reticle support 47. A magnified image of the work-piece 14 is formed on a screen 27 by an objective 23 and fixed lens 22; the latter is preferably positioned adjacent the aerial image and forms an image of the stop 18 of the afocal system 16, 17 at the stop 24 of the objective 23. This objective and fixed lens are mounted together with other objectives and fixed lenses in a turrent 30 rotatable by an external knob 34 so that any one of said objectives may be used at a time. Behind the screen 27 is mounted a Fresnel lens 28 and clips 46 are provided to hold on the screen a master chart for comparison with the workpiece image. As shown in Fig. 3, the workpiece may be illuminated episcopically by a lamp 50, light from which is reflected by a mirror 52 and annular reflector 18 on to the work-piece, the light reflected thereby passing through the first lens 16 of the afocal system of Fig. 2 and then through the aperture in reflector 18, which forms the stop of the afocal system. In another form, the work-piece is illuminated by a source disposed thereabove, an inclined reflector being mounted beneath the work-piece to direct the light into the comparator. Optical data are given for examples of the first and second objective systems.