| 摘要 |
<p>A point focus thin film Fresnel lens (15; 25) has an inner, substantially flat region (8; 22), and an outer region (9; 23), the outer region projecting outwardly from the inner region and at a substantial angle away from the plane of the inner region. In one embodiment the lens is in the form of a truncated cone (15) with a circular inner region as its apex, hi another embodiment the lens is in the form of a dome (25) and the outer region is formed by joining together segments (23) extending radially from a circular central region (22).</p> |
