A Fresnell lens and filter are disposed in a frame adjustably pivotally attached to a bar extending from a cabinet having a viewing screen for a computer, e.g. The bar is movable to adjust the distance of the lens from the screen and the height of the lens relative to the screen. A clamp for the bar...http://www.google.se/patents/US4712870?utm_source=gb-gplus-sharePatent US4712870 - Fresnell lens and filter for use with computers and the like
