So, I got bitten by the IR dongle bug not so long ago, after it dawned on me that modern thermal dongle are better than the thing Predator 1 and 2 was filmed on.
I always wanted one, but the limitations of hardware (and lack of my personal skills) kept me at arms length from dongles, until now.
After I conquered the PC to HikMik Explored E20+ interface thanks to helpful hands in DYI Thermal Imaging Discord, I started to expand my repertoire of what i can do with this wonderful little device.
The limitation of this device are obvious. Its meant for outdoors, fast refresh rate and good contrast but more or less unreliable temperature readings. And that is fine, I got it for pushing limits, not finding grid faults.(tho i am thinking of putting a poster on local boards for "thermal scan for leaks, call XXX-...", we got -30 winters here in Scandoland, a quick coldspot sweep out and in will find the worst faults, and handheld spotter can take accurate readings, but i digress.) Despite the dongle being meant for long distances, mostly, it has respectable macro capability thanks to the manual focus. In a pinch you can use it as a fault finder and spot that 2mm SMD resistor heating up on a laptop PCB no problemo. It has respectable range in
spotting human-sized objects, on a winter backdrop, over a lake, I have managed to see humans roughly 500m away.
Identifying humans, reliably, begins at 200m, now you can tell human from a large dog 99% of the time. Identifying gender start 100-70m and you can start distinguishing facial features from 20m, the mouth and smiling face will start to resolve.
So, now that I got a good feel of what this thing can do unaided, its time to see what i can do with some Aliexpres parts. I got a pair of CVD D12mm F38.1 meniscus ZnSe CO2 laser focusing lenses and a Acuter Newtony D50mm 200F f/4 Newtonian telescope and went to town. I tried to do some math and use
this site's wonderful simulator for planning, but most calculations I did was more or less back of the napkin. The AR coating alone would need a more professional program to model. Needles to say, I struggled to get it all work for a while. Firstly, I tried Mittenzwey configuration, but ended up going with Ramsted as it boosted the FoV and cleared the image by removing most of the IR noise from the focus. Both configurations worked fine as a IR microscope, I could get amazing IR closeups, way beyond anything useful, as the heat will equalize in its surroundings and the use cases would... limited to something that had good surface for emission and low conduction to surroundings, small ceramic parts maybe?
The telescope part was initially a hot mess, in all the meaning of the word. I had huge hot halo and clod center, indication of all sorts of stray light getting in to camera. After a long fight, trial and error, I finally managed to increase the image quality by adding apertures to cut off some of the telescopes own noise and limiting possible reflections between eyepieces. Tin foil worked the best, as it reflected most stray IR away and metal surfaces themselves are not as IR noisy unless you catch reflection from them. The magnification is roughly +-7x, I took a picture from 7m away at my hot kettle that is 20m in diameter and was about 2 degree in angular size. It was then magnified by the telescope to fill the whole FoV, that is roughly 14 degree. Not bad! I was also pleasantly surprised, that the mirror could still gather enough IR to show the paper towels against background, but very faintly.
Next step will be getting some
first surface gold coated D50mm F100mm spherical mirror to replace the one that came from Acuter. Finding gold coated secondary mirror has proven difficult. I am also thinking of adding some baffles and maybe Peltier coolers with heat-pipes to cool the optics, holders and mirror to sub ambient (some sensors+ logic to keep temp above dewpoint). If any one of you fine gents have tips or ideas, I am all ears!
So, here are some pictures from my toil and labor.
picture 1 and 2: Eyepieces
picture 3 and 4, the telescope
picture 5 is camera's own macro, 6 and 7 are the microscopic pictures with eyepiece
and the moneyshot 8 and 9: the pot and pot trough telescope