I want to place 2 camera lenses (eg Thorlabs MVL12M23 and MVL50M1) inside the inner vacuum can of an Oxford Kelvinox MX250 dilution cryostat. The camera lenses will be thermally connected to the helium bath and will sit at around 4.2 K. They will be brought to this temperature over the course of a few hours. I intend to set the lenses to infinity and maximum aperture, then never adjust them again. They will be used facing each other in a tandem setup, similar to this article: 10.1016/0165-0270(91)90038-2.
I am interested to know if these lenses would become unusably damaged during the cooling process, and if so, what the damage mechanisms are and how I might avoid them?
If you cool and warm up slow enough, the actual glass pieces of any lens (objective) would normally survive, but the contracting aluminum mounting would normally kill them. Also color corrected glued together double lenses would normally brake, since the two glass types expand and contract differently.
You are on the save side, if you use any set up of quartz-glass lenses, mounted each via a thin foil (best from stainless steel) that would limit the stress caused by different expansion coefficients of the involved materials.
Have fun and good luck (the latter is not really needed, since I used the recommended method quite often)
Wolfgang Grill
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