Aspherical lens elements

The three rear lens elements are to be used at cryogenic temperature, and the manufacturing specifications must account for both the change in index of refraction and the geometric contraction with temperature. This is straightforward for the spherical surfaces but not for the asphere. Li practice, the problem was solved by manual iteration. Trial lens constants were supplied, and the sag after thermal contraction was calculated and compared to the sag desired. Adjusting the constants eventually led to a lens that will contract to the desired cold shape. 

Fig. 2.4 Some spherical and aspheric discrete microlenses for optical concentrators in MWIR and LWIR range that may be fabricated by microsystem technologies, a calotte b hemisphere c hyperhemisphere d ball lens e truncated sphere f bulb g hemi-cylinder h cylinder i curvilinear cone j concave concentrator k gradient-index lens (GRIN) I complex two-element lens (sphere/GRIN). The grid corresponds to the homogeneity of refractive index, i.e., describes its gradient...

The camera lens is a barium fiuoride, lithium fiuoride achromat that focuses the collimated light onto the detector. The filter wheels are place at sudi an angle to the collimated beam that any light refiecting off the detector will not hit the array if it is specularly reflected from the filta surfaces. The lens consists of two thidc elements with all four surfaces being diamond tinned aspheres. 

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