OPTICAL MEANS FOR ANNULAR ILLUMINATION OF A SPOT

摘要

An optical system operable to focus an annular beam of light onto a spot 16 comprises a paraboloidal reflector 10 with a lamp 12 at its focus, a coaxial annular convex lens 13 and a coaxial internally silvered conical mirror 15. A parallel beam of light formed by reflection by the reflector 10 of light from the lamp 12, if formed into a convergent annular beam by the lens 13 and reflected by the mirror 15 which is located between the lens 13 and its focus so that it converges to the spot 16.