Lost my thermal expert lens cap - now what?

[morningglory747]

Salutations,

A few months ago I purchased a T.E - Q1 camera with an additional 13mm lens for a work related project and now it seems as though I can no longer find the darn lens cap. Unfortunately, I did not place them within the carrying case following my last usage. Through the official i3system website, I could purchase new lens cap, but just the shipping itself would cost 65$ and for such small little things, I feel like that doesn't make it worth it. I've read through this post a few times : https://www.eevblog.com/forum/thermal-imaging/sub-10$-black-body-for-sensor-calibration/ but i'm not sure I correctly understand whats being said. What Frenky did doesn't seem to be good because it's a cavity blackbody (in the case of the tennis ball) and there's not a uniform spread of temperature (in the case of the tin case). Consequently, what I understand from this is that the lens cap provided by the i3systems is the best thing for the sensor calibration. Before making the purchase, I would like to confirm if this is the 'only true solution' to get a proper sensor calibration or if there's some sort of knowledge unbeknownst to me that would allow me to improvise something a reasonable price without disturbing the readings too much?

On the topic of calibrations, I have another question. My current interest with the TEQ1 camera is to read flower temperatures outside during the end of spring time. My last project was a failure as two different pictures of the same object had considerable temperature differences. One possible solution is by handling a potential shutter problem, where it seems like I need to let the camera rest a while before using it. The second solution is that I have a black body reference who's temperature is known through another temperature reading device within the frame of the picture. As such, I would be able to correct the camera readings in the eventuality of a drift. Would anybody be aware of good black body reference that I could use? I was thinking that maybe I could use a mason jar filled with water whose temperature I could read through some electronic thermometer. Would that be a sufficient comparaison tool?

Thanks!

[frenky]

I am well aware that with posting my diy projects on this forum I expose myself to critism from people who do not actualy make anything. I can live with that because usually pepople who find it useful are just reading and dont post a reply to thread.

But it does saddens me when  the idea/project gets completly devalued in the eyes of random reader because of this criticism.

If you think that shiny metal cap which is reflecting sensors heat back onto it is a better calibration tool than diy black cavity that doesent, then you should just pay for the postage and buy the cap...
(And do not hold it with your hands because you will introduce thermal gradient on its surface.)

[morningglory747]

My apologies. Devalorising your work was not the outcome I was seeking and consequently I have shown an important lack of wisdom. I will take this as a lesson for the future.

[Fraser]

@Frenky,

I just read your comment and felt very guilty indeed  I hope my comments on your $10 tin black body thread have not caused you concern or offence. If so, such was not intended. I was just offering some comment based on my long term use of all manner of thermal imaging systems. Black bodies are something that I did quite a bit of work with and I own a few.

To the OP,

To answer the OP's questions. A lens cap based Flat Field Correction process requires the lens to be covered by a material that presents a nice thermally flat 'scene' to the sensor array via the lens system. A lens cap may be constructed of metal of non-metal materials but it is important that it is opaques to Long Wave IR and that its surface facing the camera lens presents a nice non reflective characteristic. Reflective surfaces can be tolerated in other black body designs, but are not great in the lens cap scenario for the reasons that Frenky has discovered.

In my personal experience I have used lens caps for FFC and dead Pixel detection purposes that were made from Aluminium that was approximately 5mm thick and coated with a high emissivity matte black paint inside. Any matte black enamel of acrylic paint would work fine though. The thickness, and hence thermal mass, of the lens cap helped with thermal gradients across the material due to brief hand holding. A thin aluminium lens cap can have a relatively fast take up of thermal energy from the fingers due to low thermal mass but such quickly drops back to ambient so is not a great problem. I have also used FFC caps made from Nylon and they also worked well.

So in precis, you do not need to buy the original Thermal Expert lens cap unless you want originality. Even then, I would make sure that its interior face for FFC is painted matte black. You can create your own lens cap for FFC events either by replicating the work of Frenky, or just buying/making a lens cap that sits over the lens and contains a metal disk that has been painted with matte black paint. If you place the metal disk inside a plastic lens cap you achieve some thermal isolation of the disk from finger heat as well.

Fraser

[frenky]

Frazer, now I feel bad for making you feel bad. That was not my purpose. (I was not targeting you...)
I have a great respect for you and your willingness to share your wast knowledge and experience.
I have learned a lot from you in the past years and hope to learn more in the future.

Posts like this one you have just made to the OP make your contributions to this forum invaluable. 

[bap2703]

Quick and dirty: use your hand.
Not quick but still dirty: a piece of velvet glued on cardboard.

[Ultrapurple]

My Therm-App lenses are never capped. Whenever I need to do a noise reduction calibration I simply put the device lens-down on whatever is handy and at ambient temperature - a desk, a wall, a book - or even simply put it against my trouser leg or coat if there's nothing suitably flat around at ambient temperature when I'm outdoors or whatever.

As long as the temperature is fairly even as seen by the lens it's OK. Small imperfections in smoothness (eg the weave of cloth) don't really matter but I'd avoid anything that has an obvious strong signature such as black print on white paper.

[morningglory747]

Thank you for the suggestions albeit my rudeness  (). I will go with Fraser's proposition as it can provide a more elaborate methodology for a potential paper on the matter.

[Fraser]

Frenky.

No harm done 

I was just concerned that my somewhat 'clinical' comments on FFC lens cap design might have been seen as criticism. That is the trouble with the written word, sometimes it can seem 'cold' rather than helpful or supportive. I love seeing creative thinking and experimentation and would never try to crush such enthusiasm 

Fraser

[morningglory747]

For those who are interested,

I contacted i3systems about getting new lens cap and they sent me the following message:

You do not need to buy extra lens cap for calibration.

You can use any mateirals that have uniformed surface such as name card when you calibrate.

regards,