Sub 10$ black body for sensor calibration - Page 1
Forum section: electronics / general

author: frenky
author_rank: Unknown
timestamp: January 02, 2019, 01:14:45 pm
content: i3system recomends using metal cap supplied with ThermalExpert for calibrating sensor.But shiny metal is reflecting sensors heat back onto it so I decided to make a cheap portable black body.The idea was to make something like this:So I took tennis ball split it in half and painted inside with 800*C black heat resistant paint:It's not pretty but it works.Before:After:

author: Ultrapurple
author_rank: Super Contributor
timestamp: January 02, 2019, 02:50:52 pm
content: Ingenious!

author: Bill W
author_rank: Super Contributor
timestamp: January 02, 2019, 05:15:52 pm
content: Any cavity should appear as a black body - even a shiny one - due to the multiple reflections inside. That does assume a big cavity and small hole. that is why black body can also be called 'cavity radiation'.This lies behind the 'tube' black bodies such ashttps://www.omega.com/pptst/BB-4A.htmlandhttps://www.opteema.com/media/ol480_cone_cavity_fhd.jpgThere is even one using a vat of molten gold as the stable temperature.Bill

author: frenky
author_rank: Unknown
timestamp: January 03, 2019, 06:33:17 am
content: @Bill: Blackbody with gold in it would really be a score on ebay or flea market...So later I've made more compact version and it seems to work as good as tennis ball.Took a tin can of peppermints:Drilled a big hole on the flush side:Painted it with mate black high temperature spray paint:Made a few round circles from craft foam and glued it together to get a hollow cylinder which fits snugly on lens:And it's done:(I could paint outside with black but I prefer this funky look)

author: Mr. Scram
author_rank: Super Contributor
timestamp: January 03, 2019, 06:43:09 am
content: Interesting. I've seen some pictures with similar striping or noise before, but hadn't realized that could actually be a black body issue.

author: frenky
author_rank: Unknown
timestamp: January 03, 2019, 06:51:09 am
content: It's not really a blackbody issue but a sensor issue. Blackbody fixes that by providing good even calibration surface.

author: Mr. Scram
author_rank: Super Contributor
timestamp: January 03, 2019, 06:58:19 am
content: Quote from: frenky on January 03, 2019, 06:51:09 amUltimately yes. Though if everything else is the same and a better black body improves the image quality, I call that a black body issue.

author: IwuzBornanerd
author_rank: Frequent Contributor
timestamp: January 03, 2019, 09:27:08 am
content: Can you wrap a heater coil inside there out of the view of the camera, warm up the inside and still get a uniform temperature across the camera's view or will the shape & position (etc.) of the heater be factors?

author: frenky
author_rank: Unknown
timestamp: January 03, 2019, 10:15:57 am
content: I can only guess. For me this is good enough.I can use precise temp meter to measure current temperature inside of a box and use that to calibrate thermal camera.

author: Fraser
author_rank: Super Contributor
timestamp: January 03, 2019, 04:15:34 pm
content: Please be aware that the tin solution is not truly a black body design, it is a reference plate with relatively even temperature across the surface. It is really still just a 'lens cap". Holding it could generate a delta T across the surface so some care is required in its use. You could achieve the exact same performance by placing a flat non reflective surface over the lens. Try Matt painting a flat piece of thick ABS plastic or metal and compare the results of placing them and the tin in front of the lens.The original lens cap solution used by the manufacturer of your camera is also used in some military cooled thermal cameras to create a flat field and detect dead pixels. The key to success is a lens cap that presents little Delta T across its surface and is non reflective to thermal energy. They are either ABS or metal and coated with a low reflectivity paint on the inside surface. Matt black enamel or acrylic paint will work fine.Cavity black bodies are really more appropriate for temperature calibration checks where either the ambient temperature or a thermal energy emission plate is in use. The cavity should obey certain dimensional criteria to be effective. A cavity is often a sphere or a tube with greater length than diameter and a cone shaped or deeply grooved flat end. Not all black body references use a cavity. Some use just the flat emission plate but these are prone to external influences are errors.Fraser

author: JimRemington
author_rank: Regular Contributor
timestamp: January 03, 2019, 04:40:32 pm
content: QuoteI imagine that not painting the outside of the tin could lead to small temperature differences inside, due to the different absorption coefficients/emissivities of the differently colored outer surfaces.

author: Fraser
author_rank: Super Contributor
timestamp: January 03, 2019, 04:52:00 pm
content: For those wanting to play with sphere type black bodies, help is at hand with correctly shaped split spheres..... bath bomb and ball cake aluminium mounds !On eBay moulds to make bath bombs and also ball shaped cakes are both cheap and easily available. They are adequate for a hobbyist black body sphere and come in a range of sizes up to around 8"https://www.ebay.com/itm/16-pcs-8-Set-DIY-Mold-Sphere-Metal-Bath-Bomb-Fizzy-Crafting-Cake-Candle-Mould/263200233764?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l2649https://www.ebay.com/itm/Sports-Ball-3-D-Cake-Pan-Basketball-Soccer-3D-Stand-up-Mold-Tin-Sphere-Cream/301807958628?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l2649Happy experimentingFraser

author: frenky
author_rank: Unknown
timestamp: January 03, 2019, 08:01:46 pm
content: In my defense...I was not trying to build something that NSA would use to improve images of spy satellites but something very compact to remove noise from my thermal photos.In the past I was using thick aluminium plate painted in mate black. But that was very unpleasant to carry around because of size, weight and fear of smudges.And sensor would still prick up reflections of sun or light bulb or human near the plate because black paint would not absorb all IR... (Vantablack would probably solve that...)This simple tin can solves all those issues for me. I can carry it with ease and make pretty photos on the go.I might add another layer of craft foam around it to better insulate it. But I don't think that will be necessary since I only hold it on the edges for a second when I put it on.So for pretty pictures my solution is perfectly fine while for professional use calibrated electronic blackbody is surely more fitting...

author: Fraser
author_rank: Super Contributor
timestamp: January 03, 2019, 08:52:22 pm
content: No criticism intended.What I was trying to suggest is that you just paint the inside of your original camera lens cap with a non reflective paint. You might be surprised at the improvement in the caps performance. Such would be an even better solution than your current tinI will just head back to my rock now and climb back under it where I can do no harmFraser

author: frenky
author_rank: Unknown
timestamp: January 03, 2019, 09:06:00 pm
content: Don't get me wrong. I always enjoy reading your posts since you really are a library of knowledge of T.I.Just have a mercy on us rookies who only want to take pretty pictures.

author: Fraser
author_rank: Super Contributor
timestamp: January 03, 2019, 09:20:58 pm
content: Fear not, I had already decided to step back and let newcomers to Thermal imaging learn from each other through the fun of experimentation and use. I promised myself I would pull back from forum activity this year in order to concentrate on my family, work and hobbies.Have a fun 2019 everyoneFraser

author: Vipitis
author_rank: Frequent Contributor
timestamp: January 04, 2019, 02:17:27 am
content: Although this topic might not be for me yet, I love the idea and creativity here. For astrophotography you can do multiple types of correction by capturing an even light, an even dark or a really short exposure and I have always asked myself how would you do this with a thermal camera which the answer is much simpler then an BEC.And Fraser, you might not want to realize, but this forum right here is part of your family, your work and your hobby; don't feel the need to go far so you can always comeback to us. This forum, which you embody, has sparked and directed my interest in unusual imaging which I am very likely to pursue further in my educational career.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: January 04, 2019, 03:08:16 am
content: You might try turning the tennis ball inside out. Usually possible and except for a curl at the cut line ends up pretty spherical. The flocked side painted black would be just about perfect for the inside of this "integrating sphere"

author: bap2703
author_rank: Regular Contributor
timestamp: January 04, 2019, 12:46:38 pm
content: That's just a flat field correction, calling it a calibration is an overstatement.Using your bare hand moving and out of focus (for maximum blur) should produce something similar, or I am missing something ?

author: EEVblog
author_rank: Unknown
timestamp: January 04, 2019, 01:21:32 pm
content: Quote from: frenky on January 02, 2019, 01:14:45 pmThat's how integrating spheres for LED lights and bulb for true lumen measurements work, except the source is inside instead of outside, and it's white instead of black.Nice.

author: eKretz
author_rank: Frequent Contributor
timestamp: January 04, 2019, 06:04:37 pm
content: Isn't what the OP is doing just more or less a manual NUC? Does that device not have one built in?

author: frenky
author_rank: Unknown
timestamp: January 04, 2019, 06:16:00 pm
content: ThermalExpert modules do not have shutter integrated because sensor readings are very stable.