Patent ID: 7712924

Claim:
A reflective iris for adjusting the F-number of an elliptical lamp, the elliptical lamp for producing a focused light beam at a given focal point having a given cone angle, the reflective iris comprising, a generally spherical convex mirror portion for retro-reflecting a high cone angle portion of the focused light beam back through the elliptical lamp, when the generally spherical convex mirror portion is in general longitudinal alignment with a light emitting aperture of the elliptical lamp and a center of the generally spherical convex mirror portion is generally aligned with the given focal point, such that said high cone angle portion emerges from the elliptical lamp at a smaller cone angle after retroflection; and an optical aperture through said generally spherical convex mirror portion, disposed around a longitudinal axis of said generally spherical convex mirror portion, for enabling transmission there-through of a lower cone angle portion of the focused light beam and the retro-reflected high cone angle portion, such that an effective cone angle of the elliptical lamp is smaller than the given cone angle.