What is an Uncooled LWIR Thermal Infrared Camera and Why is it ...

Uncooled LWIR infrared imaging cameras are the most common type of thermal cameras, as they more affordable than cooled MWIR thermal cameras. In addition to the upfront costs of the camera being more affordable, uncooled thermal cameras require no cooling, which means no regular cryocooler maintenance or replacement as is the case with MWIR cooled thermal cameras. Infiniti’s LWIR camera systems boast better images than most of our industry-leading competitors as we pair our uncooled sensors with large aperture germanium lenses, allowing more thermal energy to reach the sensor, which results in a cleaner and sharper image.

If you want to learn more, please visit our website.

Infiniti uses cutting-edge 12μm LWIR VOx uncooled thermal sensors with resolutions from 384×288 up to × HD. The 12μm pixel pitch provides a narrower field of view without changing the lens. This means we are able to achieve 40% further range than 17μm sensors and 25% further range than 15μm sensors while delivering a thermal sensitivity of 0.05°C.

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Ultrapurple

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Plastic lenses for LWIR?

« on: September 20, , 11:04:10 am » Has anyone tried using plastic Fresnel lenses for thermal imaging?

For a long time I've been mulling over the multi-zone lenses on the front of PIR security sensors but then found that a few manufacturers produce lightweight Fresnel lenses that are supposed to be able to "replace expensive germanium lenses in systems requiring moderate imaging quality".
See http://www.kube.ch/downloads/pdf/kube_single_fresnel_lenses.pdf from Kube Electronics AG, Switzerland.

On the face of it, a 13.5mm FL f/0.5 (!) lens made from 0.5mm thick HDPE with ~70% transmission at 10µm looks quite attractive - and a lot cheaper than germanium. But their idea of 'moderate imaging quality' may be different from mine.

I asked about prices of a couple of the lenses and the answers were in the 10 to 20 euro range, plus 24 euro for P&P. (All very reasonable for one-off sample sales, I reckon).

Thoughts?


« Last Edit: September 20, , 02:59:31 pm by Ultrapurple » Rubber bands bridge the gap between WD40 and duct tape.

Fraser

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Re: Plastic lenses for LWIR?

« Reply #1 on: September 20, , 03:01:38 pm » The use of thin fresnel and diffractive lenses made from LWIR transmissive material for thermal cameras has been considered over the years. There is at least one company that took the idea of using plastic fresnel lenses into production for relatively low resolution tasking. From what I know of the plastic fresnel lens product, it is very 'course' and created a poor thermal image on a 320 x 240 pixel core. Diffractive lenses using ZnSe and Silicon have produced affordable and good quality imaging lenses. The plastic lenses have some way to go in terms of technology before they can be considered a serous alternative to conventional silicon, ZnSe, ZnS and Germanium optics. There are diffractive Silicon and ZnSe lenses that work very well at limited resoloutions. The TAU2 has a diffractive ZnS rear lens element and the LEPTON cores use Silicon diffractive lenses.

I was looking at using the plain (non fresnel) PIR windows as lens protector material. It's transmission losses seemed quite high compared to the thin shrink film that I normally use. A PIR is looking for a 36C target against a approx 22C background. The two or four pyroelectric detector elements are huge compared to a cameras microbolometer pixels. Transmission losses can be quite high in such a design and it will still work.

I would like to track down more affordable ZnSe lenses of greater diameter than 20mm and greater FL than 100mm. They would be useful for supplementary lenses. For me, plastic fresnel lenses is not the way forward at the moment.

Fraser « Last Edit: September 20, , 06:59:23 pm by Fraser » If I have helped you please consider a donation : https://gofund.me/c86b0a2c

Vipitis

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Re: Plastic lenses for LWIR?

« Reply #2 on: September 22, , 02:04:23 pm » Is there any source where I could get such a cheap lens?

My Lepton isn't high resolution anyways, but I want a telephoto lens to shoot the moon, the stock the fov is really wide.

Ultrapurple

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Re: Plastic lenses for LWIR?

« Reply #3 on: September 22, , 02:23:58 pm » I have some of these plastic lenses on order and will test them with my Therm-App, which has easy access to the sensor. I will report what I find, though I strongly suspect Fraser is right and the results will be at best mediocre. Rubber bands bridge the gap between WD40 and duct tape.

Fraser

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Re: Plastic lenses for LWIR?

« Reply #4 on: September 22, , 04:24:01 pm » Ultrapurple,

I will be very interested to hear what you think of the lenses.

A source of these lenses is decent quality IR Thermometers where they are often used to focus the energy onto the thermopile sensor.

Thank you for spending your money investigating these lenses. It is a pity the company does not offer a free sample as they are not expensive to produce once the press mounds are made.

Fraser « Last Edit: September 22, , 06:35:57 pm by Fraser » If I have helped you please consider a donation : https://gofund.me/c86b0a2c

Fraser

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Re: Plastic lenses for LWIR?

« Reply #5 on: September 22, , 04:44:27 pm » This may be of interest.....

http://www.fresneltech.com/thermalimaging.html

$350 per lens in quantities of 5 though ! Ouch 

Fraser « Last Edit: September 22, , 04:47:29 pm by Fraser » If I have helped you please consider a donation : https://gofund.me/c86b0a2c

Ultrapurple

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Re: Plastic lenses for LWIR?

« Reply #6 on: September 22, , 05:06:56 pm » Ouch indeed! I'll play with my 12 euro lenses first, I think.

Interesting that they say they work best with large-pixel (50µ) cameras, presumably because the MTF is poor. Rubber bands bridge the gap between WD40 and duct tape.

Fraser

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Re: Plastic lenses for LWIR?

« Reply #7 on: September 22, , 05:41:49 pm » I believe it comes down to the resolution of the lens itself. A Fresnel does have resolution limits.

https://en.m.wikipedia.org/wiki/Optical_resolution

The large microbolometer pixels are more forgiving of such but that makes the sensor die and associated lens system larger for say a 320 x 240 pixel microbolometer. 50um pixels were found in BST sensors and early Microbolometers, as used in the Indigo Alpha camera etc. I suspect that there are not a lot of 50um Microbolometers in current production.

Fraser If I have helped you please consider a donation : https://gofund.me/c86b0a2c

Fraser

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« Last Edit: September 22, , 06:49:19 pm by Fraser » If I have helped you please consider a donation : https://gofund.me/c86b0a2c

Ultrapurple

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Re: Plastic lenses for LWIR?

« Reply #9 on: September 25, , 11:08:21 am » The lenses have arrived, as of Monday 25 September. I have 13.5mm, 25mm and 59.4mm focal lengths. Initial experiments show that they will form images on the Therm-App sensor, but the efficiency (=contrast) is relatively low.

Whether the lenses can be contrived into something that's actually useful remains to be seen. I'm not in a position to do any proper experimentation during the day - lunchtimes are very short - but I will have a play and see what I can achieve over the next few days. I do wonder about making an x4.4 Keplarian telescope with the 59.4 and 13.5mm lenses, but suspect the losses would be prohibitive. It certainly wouldn't be a patch on my germanium x3 telescope!
« Last Edit: September 25, , 11:31:22 am by Ultrapurple » Rubber bands bridge the gap between WD40 and duct tape.

Fraser

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Re: Plastic lenses for LWIR?

« Reply #10 on: September 25, , 12:26:44 pm » I bought an Inframetrics 48" FL Germanium close-up lens from the US that is currently on its way to me.
It was very cheap so I thought I would experiment with it. It is just the meniscus lens element but is the same as my Inframetrics 6" and 12" FL Close-up mounted lenses.the 48" FL is HUGE for a telescope but I thought I might try it for a laugh  the lens diameter is around 60mm so not a huge aperture. Mating it with a 15mm FL Germanium bi-convex lens that I have could be interesting though  The losses will likely be huge. A 80x magnification Keperian telescope using a mm and 15mm FL lens....... I do not think it is that easy