GB1528929A - Louvred echelon lens - Google Patents

Abstract

1528929 Internally louvered echelon lenses MINNESOTA MINING & MFG CO 7 Oct 1975 41098/75 Heading G2J An echelon lens has at least one surface 15, Fig. 1, configured as a linear array of echelons, and has within its thickness a plurality of internal light blocking louvres 13 separated by transparent portions 12, the arrangement of the louvres being such as to allow light to pass through the lens from one side to the other, but to absorb scattered and reflected light which would otherwise degrade the contrast, and the angle between the direction of the louvres and the echelons being chosen to reduce moire fringes. The louvered layer is preferably skived from a block composed of alternate transparent and opaque layers and is subsequently laminated between transparent facing layers, e.g. 14, Fig. 1, one of which may be the configured layer 15. Alternatively the configured layer may be attached at a plurality of periodically spaced points (e.g. by adhesive as per Fig. 4, (not shown); or by engagement of studs with sockets in the louvered layer, as per Fig. 3, (not shown). The moire fringes may be eliminated by having the louvres and echelons exactly parallel, or by ensuring a sufficiently large angle therebetween (e.g. more than 10 degrees). The louvres (as seen in a lens cross section) may be arranged so as to 'fan out' to allow light required for refraction to pass through the echelons. In one form, the louvred layer has a configured surface on either side, with the respective linear echelons being arranged at right angles. Such a lens can achieve a point focus (as opposed to a line focus for a single linear echelon). Specification 1253237 is referred to.