| 摘要 |
<p>The Fresnel lens assembly (8) carries on both its faces a number of concentric grooves whose angles a,b,c and d of the groove walls are functions of the distance 'u' of the wall from the lens axis of symmetry and the radius 'r' of the lens. The lens assembly may be formed by two Fresnel lenses, plane on one side, with the grooved sides facing one another, or a single lens protected on each side by a respective plane transparent piece. The assembly is conveniently used for enlarging images provided by e.g. a television screen.</p> |
