[David Prutchi] writes in to tell us about his recent experiments with building lenses for thermal imaging cameras, which to his knowledge is a first (at least as far as DIY hardware is concerned). With his custom designed and built optics, he’s demonstrated the ability to not only zoom in on distant targets, but get up close and personal with small objects. He’s working with the Seek RevealPro, but the concept should work on hardware from other manufacturers as well.
In his detailed whitepaper, [David] starts by describing the types of lenses that are appropriate for thermal imaging. Glass doesn’t transmit the wavelengths that thermal camera is looking for, so the lenses need to be made of either germanium or zinc selenide. These aren’t exactly the kind of thing you can pick up at the local camera shop, and even small lenses made of these materials can cost hundreds of dollars. He suggests keeping an eye out on eBay for surplus optics you could pull them out of to keep costs down. Jgs2
Creating the macro adapter is easy enough, you simply put a convex lens in front of the thermal camera. But telephoto is a bit more involved, and the rest of the whitepaper details the math and construction techniques used to assemble it the optics. [David] gives a complete bill of materials and cost breakdown for his telephoto converter, but prepare for a bout of sticker shock: the total cost with all new hardware is nearly $500 USD. The majority of that is for the special lenses though, so if you can score some on the second-hand market it can drop the cost significantly.
We’ve seen an impressive array of thermal camera hacks and projects recently, no doubt due to the falling prices of consumer-level imaging hardware. Given their utility as a diagnostic tool, a thermal camera might be something worth adding to your bag of tricks.
Nice! But would be so much cheaper if ZnSe optics from Aliexpress for CO2 lasers would be used! They work perfectly fine (yes I tested it) The lens tube etc could probably be 3d printed.
https://www.aliexpress.com/store/product/USA-IIVI-ZnSe-Focal-Lens-for-CO2-Laser-Cutting-Engraving-Dia-25mm-FL-3-76-2mm/1266435_32610599440.html here ya go… still 60USD but you can get cheaper ones… the quality is not as good though. It’s also quite handy that they come with a BBAR coating optimised for 10.6um. GaAs lenses could be used and might be better for the front lens as they are harder.
Indeed. There is no reason (i can see) that would prevent that. 25mm Znse are ~30 usd, a 12mm would be much cheaper.
The whitepaper does mention “Far-East Offerings” as a possible source of lenses, so probably that’s what he’s referencing.
Indeed, my blog posting discusses both ZnSe and Ge lense in some detail, and specifically mentions that cheap CO2 laser lenses are equally suitable.
PS. Detailed instructions on the selection of Ge or ZnSe lenses, possible sources, as well as complete construction instructions are on the paper that can be downloaded from: http://uvirimaging.com/wp-content/uploads/2018/03/Diy-Thermal-Camera-Telephoto-Converter.pdf
Can you use sapphire or NaCl lenses? Salt was a standard in IR spectrometers in the old days.
Sapphire probably no because its short-pass cutoff is at around 5um, whereas common thermal imagers work in the ~8 to 12 um range. NaCl yes, but I haven’t seen one since I built my first CO2 laser back in highschool some 35 years ago… They degrade very quickly with environmental moisture, and have been almost completely replaced by ZnSe for CO2 lasers, although I know that they are still used in some specialized IR spectroscopy systems. Potassium Bromide (KBr) is another possible choice, although, again, it’s very sensitive to moisture.
Interesting. I recall replacing Nernst Glowers in Beckman spectrophotometers that use optical choppers. Also working on temperature sensors for RTP wafer processing. They looked at the bottom of the wafer through a 100mm sapphire rod. I didn’t think they worked very well at the time, and the people making them did not know how they worked. However, there is one in every Intel “copy exact” RTP setup.
That’s a pretty common approach for basic macro lenses.
True for macro magnifiers, but I searched high and low for information on telephoto converters, and all I could find is a YouTube video in Russian at: https://www.youtube.com/watch?v=rt4EHTFfKVw&t=38s
I am not a Russian speaker, and I couldn’t find any other details on how he built the telephoto that he shows in the video, although there are a few pictures with no further explanations at: http://www.eevblog.com/forum/thermal-imaging/yet-another-cheap-thermal-imager-incoming/msg721312/#msg721312. Boris has other videos on his thermal cameras that look very cool: https://www.youtube.com/channel/UCCWd-19-oYdUmPMR8V0TchQ
The 3D printed parts that Boris shows in his video do look very nice, so I’ll try to get in touch with him to encourage him to post details and maybe stl files.
Oh man this is a very interesting post. I’m in the middle of preplanning a multi-wavelength imaging setup and was curious about what optics I need for the longer wavelengths as glass blocks them.
Thanks! If you are interested in imaging outside the other side of the visible spectrum (MW and SW UV), please take a look at the following post: http://uvirimaging.com/2016/07/03/diy-shortwave-uv-image-converters-for-solar-blind-and-ruvis-imaging/
Just some things to keep in mind: The laser optics are all designed for 10u, tow peaks 9.4 and 10.6. They are not chromatically adapted for the LWIR range of 7u to 15u. You can build a system using this, but the chromatic aberrations would likely limit performance. Further most of these optics have an F number of >2, typically F3. This is in most cases not suitable for uncooled IR detectors. These bolometric detectors are all designed to work with F numbers below 1.8, ideally F1.4. It is an interesting concept, but far from ideal
Agree. One of the pictures in the whitepaper shows the aberrations that you get even when using Ge lenses with AR coating for the thermal IR range. It’s OK for qualitative imaging, but some corrections would be needed for radiometric measurements. Cheers, David
hi. im a complete newbie to lenses and photography. i do have a seek reveal pro though. i’m trying to find the right lenses but im very unclear what specifications i need in terms of diameter and focal length. i found this one https://www.ebay.com/itm/1-inch-diameter-HAND-POLISHED-Germanium-Metal-Disk-99-999-5grams-Element-Sample/232258898858?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2055119.m1438.l2649. Does that work? Can you give me any newbie guidance? thanks!
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