Cryogenic (SWIR; 0.7 – 2.5 µm) infrared cameras are specialized. For astronomical purposes thermal radiation from a room-temperature lens would swamp the signal beyond 1.5 µm. To deal with this signal such cameras at low temperatures (say 120 Kelvin). The set of materials that is transmissive to 2.5 µm with *well known* indices of refraction at 120 K is quite small.

Thus, as a starting point for camera designers I provide an example lens. This all-spherical lens has an accessible (real) entrance pupil that is 150-mm in front of the first element. This 177-mm f/1.33 camera only uses CaF2, ZnSe and S-TIH1 (first negative element) yet achieve spots that are better than 5.4 µm in RMS radius! It drives a 2048 x 2048 x 18 µm pixel detector (with a 52-mm-diameter full field).

Please let me know if this design helps get you started.