| 摘要 |
The afocal telescope (20), working in the infra red light waveband, has a three-part lens (40) where the center lens (F) has a positive refraction between two lenses (E,G) with a positive and negative refraction. The side lens (E) with a positive refraction is towards the intermediate image (D) and has a hybrid surface (6) for a simultaneous correction of length and field color. One lens (F) with a positive refraction in the lens group (40) is of a material with a negative temp. refraction index coefficient, and pref. of thallium bromoiodide. It has a selected optical strength to render the telescope insensitive to heat. The lenses can be of germanium or gallium arsenide.
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