GB550870A - Improvements in or relating to optical systems - Google Patents

Abstract

550,870. Lenses; projection systems. TAYLOR, TAYLOR & HOBSON, Ltd., and WYNNE, C. G. July 22, 1941, No. 9250. [Class 97 (i)] In an optical system for profile projection comprising a front convergent member A consisting of a divergent component spaced between two convergent components, any of which may be compound, and also a compound rear member B constituting a field member, and arranged so that the distance between its front surface and the rear surface of the front member is greater than half the equivalent focal length F of the whole system, the radius of the surface R, lies between 755 F and 3.0 F; if R 5 is less than 1.75 F, the power of the surface R 8 may be greater than .25 times the power of the whole system. The member B may comprise a collective element cemented to a divergent element, either element being in front, or may, in addition, comprise a separate convergent element close to or in contact with it. Each member may be separately achromatized, and the whole system is corrected for spherical aberration, coma, astigmatism, field curvature, and distortion. The system may be used in conjunction with a small light source D and a collimator E for projecting an image of a screw thread C on to a screen G, the axis of the collimator being variably inclined to the axis of the lens system at an angle appropriate to the helix angle of the screw. The exit pupil of the system lies within or near the front of the member A and stop F. formed by an image of the light source or by an actual stop, may be located at the exit pupil. The stop F may be elongated and of variable size, and the collimator may be pivoted about a point in the optical axis of the lens system. Data for six examples of the optical system are set out. Specification 444,350 is referred to.