(under subclass 642) Subject matter wherein the lens is designed with the effective focal length equal to or greater than the distance from the first refracting surface to the focal plane.
(1) Note. This lens system is physically shorter than its rated focal length.
(2) Note. The focal length is the distance from the principle focus (focus of parallel rays of light) to the surface of a mirror or the optical center of a lens.
(3) Note. A focal point is the point at which a lens or mirror will focus parallel incident radiation.
SEE OR SEARCH THIS CLASS, SUBCLASS:
643+, for eyepieces.
648+, for projection type field curvature shaping lens. 656+, for microscope objective.
672, for selective magnification.
676, for variable magnification.
680+, for reverse telephoto lens.
708+, for a nonspherical lens.
733+, for multiple component lenses having a reflecting element.
749+, for reverse telephoto lens.
754+, for multiple component lens systems generally.
