Afocal telescope
An afocal telescope operating in the thermal infra-red waveband has a three-element objective comprising a positively-powered central lens element disposed between positively powered and negatively powered lateral lens elements, the positively powered lateral lens element being located proximal to t...
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| Format: | Patent |
| Sprache: | eng |
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| Zusammenfassung: | An afocal telescope operating in the thermal infra-red waveband has a three-element objective comprising a positively-powered central lens element disposed between positively powered and negatively powered lateral lens elements, the positively powered lateral lens element being located proximal to the inter-mediate image and incorporating a hybrid surface simultaneously to correct longitudinal and field colour, and wherein one of the positively powered lens elements of the objective is made of a material having a negative temperature refractive index co-efficient and has an optical power selected to render the telescope athermal. |
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