| 摘要 |
A spherical lens element and a concentric lens element receive light, in that order, from a wide field of view, and diverge all rays so that upon leaving said concentric element, the angles of all rays approximate that of radial lines. This light is then filtered through a concentric narrow bandpass filter to attenuate undesired background light, and is collected by a suitable light collector and detector. Apertures for selecting the field of view and F number are provided.
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