AN EXACT CONSTRAINT ARRANGEMENT FOR AND METHODS OF MOUNITNG AN ELEMENT SUCH AS A LENS

摘要

An element, such as a lens, is mounted on an element holder, such as a lens holder, so as to be constrained with a clearance-free, exact centering fit. The element has three radial faces spaced 120° apart with respect to the center of the element, and the element holder has three abutments spaced 120° apart with respect to a center point about which the abutments are distributed. Upon seating the element in the element holder with the radial faces and abutments in engagement, the element is constrained with the center points of the element and element holder in alignment. The radial faces and abutments are held in engagement by a retainer which also holds the element on the element holder. In accordance with one embodiment of the invention, the element is a plastic lens, and the element holder is a lens barrel, the lens being retained with clearance within the lens barrel by a retaining ring. Since the lens is engaged radially, rather than peripherally, the lens is free to expand and contract radially within the barrel.