| 摘要 |
The invention relates to a compact infrared passive athermalized and achromatic telephoto lens arrangement. More particularly, a lens arrangement is divulged for high resolution infrared imaging with effective focal length EFL and overall length OL, comprising one convergent front group and one divergent back group, characterized in that: the front group comprises one or more lenses forming a convergent system having an equivalent thermal glass constant gammar of less than 40.10-6 K-1; the back group comprises one or more lenses forming a divergent system having an equivalent thermal glass constant gamma T of more than 70.10-6 K-1; and, the separation between front and back groups is more than 0.45 EFL, and OL / EFL < 1.05. Combining the proper choice of lens materials for the convergent and divergent groups allows for the passive compensation of thermal drift. Further compensation can easily be achieved using a short plastic expansion ring in the lens mounting. The complete lens arrangement is particularly compact. A fast, high-resolution and drift-free telephoto lens can be obtained, while using only 2 lenses. |
