Patent GB-498458-A (GB)
Title: Improvements in or relating to optical testing or measuring apparatus
IPC: G02B21/00
Filed: 1937-06-02
Abstract: 498,458. Optical testing-apparatus. KAPELLA, Ltd., WARMISHAM, A., and REASON, R. E. June 2, 1937, Nos. 19541/38 and 19542/38 (both divided out of 498,382), and 19543 /38. [Class 97 (i)] Optical apparatus for measuring or testing the accuracy of plane or curved section profiles of hollow objects, e.g. internal screw threads, comprises means for directing a beam of light bounded at least on one side by a sharply defined plane or curved surface, with the aid of reflectors, on to the internal surface under examination, and projecting, with the aid of the same or other reflectors and an optical projecting device, the section profile on to a screen or photographic plate. Light from a source B passes through a condensing lens B<1>, and a small aperture B<2> at the focus of an objective B<3>, from which parallel light passes through a slit B<4> to a reflector A<1> and thence to the internal surface of a nut A to define a section profile thereon. The section profile is projected by means of the reflector A<1> and lens B<5> on to a screen B<6>. The lens B<5> is arranged so that its nodal planes respectively intersect the reflection of the section plane and the plane of the screen in two parallel lines equidistant from the optical axis of the projecting lens. The image on the screen is distorted owing to the oblique projection. The screen may be replaced by a photographic plate, and the photograph may be measured or enlarged. In a modification, Fig. 3, not shown, a knife edge is focused on the object, and the projecting device comprises a wide angle lens with its optical axis perpendicular to the reflection of the section plane, the rays passing obliquely through the lens. Alternatively, the oblique projecting device described in Specification 498,419 may be used. In a modification, Figs. 4 and 5 (not shown), a combination of reflectors within the hollow object is used. In Fig. 6, the illuminating and projecting devices are carried in casings E, F supported on a base G by clamps G<1>, G<2>. The illuminating device is described. in Specification 498,377, and comprises a lamp E<1>, condenser E<2>, knife edge E<3>, which may be the edge of a section of a counterpart of the object, i.e. a threaded bolt, and a lens system E<4>, E<5>, E<6> for focusing the knife edge on the surface of the nut. The lens system is such as to give an image free from distortion. The projecting device comprises an inclined support F<1> for a screen or plate and a similar lens system F<2>, F<3>, F<4>. Prisms H<1>, H<2> are closely surrounded by a nut carrier which positions the nut correctly. The diffused light from the surface of the object is used for the projection, and to avoid interference by light reflected from other parts of the object, the illuminating beam may be polarized and a crossed analyzer inserted in the projecting beam to cut out the reflected light which is still polarized while transmitting the diffused depolarized light. This arrangement is applicable to all the modifications described. Specifications 412,179, 498,382, 498,420, and 498,378 also are referred to.