Interesting experiment.
I purchased a used reflector type telescope from the local Charity shop for just such experimentation but have had no time to play lately.
I recommend that you do not remove your E4 lens as dust on the micro-bolometer is a real PITA to sort out.
You may be interested to hear that Inframetrics used to offer a thermal camera telescope based on the compact reflector lens structure often found in physically short, high magnification SLR telescope lenses. I will see if I can find a picture of it.
Sadly SLR reflector lenses are of no use as they use a reflector that may or may not be surface metalised and glass lenses are used in the design to shape the image for the camera body. Pity.
UPDATE: Pictures of Inframetrics X10 reflector lens added. Expect to pay in the order of $1500 for such a lens, and that is very cheap considering its original price !
Nice Images, thank you!!
You are right that SLR lenses can be of no use, since usually
have refractive elements in the path.
I was thinking to cheap Newtonian telescopes, that have
reflective only optics. The downside of these optical arrangements
is that are bulky, and not well corrected for field flatness, coma or
spherical aberrations. But long wavelengths are more forgiving
than visual, and a small sensor like the one in E4 will see a flat field.
It remains to be seen the behaviour of these mirrors on thermal IR.
I updated my previous post with a quick test, using an "ocular" lens.
I'm confident that direct imaging (without E4 lens in the way) will
give good results, but the dust on the bolometer is a big danger.
I definitely need to find a cheap thermal imager for experiments,
my E4 is needed to be in perfect shape for all other things.
Unfortunately my alerts on ebay for firefighting cameras arent
showing much hits.
Mike: I made a 100GPB offer, who knows