| 摘要 |
1,253,237. Overhead projections; light shields. MINNESOTA MINING & MFG; CO. Nov. 13, 1968 [Nov.14, 1967; March 11, 1968(2)], No.53893/68. Headings G2A and G2J. In an overhead projector a glare shield 22 is placed between the transparency support stage 15 and the Fresnel condensing lens 19, the shield comprising a transparent matrix of closely spaced opaque thin parallel louvres 24, 25 having an aspect ratio of between 2 and 4. The louvres may be perpendicular to or inclined to stage 15, and the panel comprising said matrix is rotated about a vertical axis to give shielding in a selected direction. Superposed transparent plastics films, each with one opaque black face, are consolidated into a solid block, and shield panels are made by taking slices from the block and mounting them between glass or plastics sheets. Another form of shield comprises intermeshing grooved transparent plates, the glare light rays being totally reflected. Again, the louvres may consist of parallel inclined grooves in a transparent sheet, the grooves being filled with non- reflective particles. The preformed shield is a flexible sheet which takes a flat bottomed trough shape within a frame. Again, the louvres may be formed as concentric rings. |
