Thermal Imaging Recommendations?

How much of a lab environment do you have? ZnSe lenses were infamous at the laser lab I worked at - I mean, sure, if you're not machining ZnSe, that reduces possible exposure to its toxicity (or rather, ZnSe releasing selenide), if you make sure you follow recommended handling advice.

But still, if something goes wrong, a lens chips and there are bits of ZnSe in the corners of your room, can you quarantine that room and make sure you get every single piece of it?

Edit: As an alternative to thermal lenses, you could set up a mirror instead for imaging - hobby astronomy supplies have imaging mirrors - those could be used to construct a thermo-optical telescope.

Edit2: There is a tutorial how to build a raspberry Pi-based reflector telescope[0]. The nice thing about it is that you don't need any second mirror or lens for looking through it - the camera sensor is in the imaging plane of the first mirror. That telescope (a 'cut' Newton telescope) could be used as a blueprint - if you want a larger field of view, you'd have to find a higher curvature mirror and adapt the telescope (a smaller design).

[0] https://pikonic.com/

Edit3: Instead of an on axis, rotationally symmetric mirror, you could use an off-axis curved mirror, like these aluminum coated ones [1], which is a cheap option. Then you can just put a thermal IR-sensor in the focal plane of the mirror and have a thermal optical setup focused at infinity (with the opticla axis going around the corner).

[1] https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=70...