Are there any add-on lens for thermal camera?

[Jenny]

Hi guys.
As you may also feel, thermal cameras are tend to have a narrow FOV, and only few of them have exchangeable lens. And it’s almost impossible to find a 3rd-party compatible lens to replace the original one, let alone the risk to do that by hand.
So are there any ways to add another lens in front of the original one, to change the focal length/FOV? I knew DSLR people did that often, but I cannot find information about thermal cameras.
Thank you.

[Fraser]

Hi,

You have not mentioned a specific camera model so this comment is generic.

Yes there are supplemental lenses available for thermal imaging cameras. They tend to be supplied by the manufacturer of the camera and have a specific mount design that attaches to the particular model of camera. The good news is that such lenses will normally work fine with other brands of camera if a mounting adapter is used. The common supplemental lenses are Wide and Telephoto. Wide is usually x0.45 and a Telephoto is X2.

It is not that easy to make your own wide angle supplemental lenses due to the limited availability and high cost of the required pair of lens elements. I recently showed a couple of AGEMA/FLIR supplemental lenses on this forum, with detail of what the lens elements  are inside them.

Sadly most supplemental lenses from companies like FLIR and FLUKE are very expensive. You are looking at Well over $1000 for most. They do appear on the used market occasionally and that is where I bought mine. They do retain their value though and prices have risen in recent years. You are looking at around $400-$600 for a used supplemental lens.

Fraser

[Fraser]

Details of the AGEMA/FLIR supplemental lenses. These are large as the PM series cameras with which they are used have large optics. Consumer grade supplemental lenses are smaller as they illuminate a smaller objective in the camera.

https://www.eevblog.com/forum/thermal-imaging/inside-flir-pm-series-tele-wide-supplemental-lenses/msg3087396/#msg3087396

Fraser

[Fraser]

My comments on the Fluke Wide supplemental lens....

https://www.eevblog.com/forum/thermal-imaging/the-fluke-wide1-10mm-f1-0-wide-supplemental-lens-use-on-other-cameras/msg2506353/#msg2506353

The FLK-Wide1 is quite common on eBay but prices vary greatly. I bought a few before the prices went up.

Fraser

[Fraser]

Some reading for you......

https://www.eevblog.com/forum/thermal-imaging/buying-used-thermal-imaging-lenses-general-buying-guidance-from-fraser/msg2955734/#msg2955734

Fraser

[Fraser]

Details of the Fluke supplemental lenses I purchased.

Fluke were running a promotion where they offered a free supplemental lens with each purchase of an expensive thermal camera from their range. People who took up the offer but did not need the free lens sold them on eBay and I bought some at decent prices. Sadly they are normally very expensive.

For information, having compared the image produced by the Fluke x0.45 lens with that produced by the official FLIR x0.45 lens on my Exx series camera, they behave the same and thexFLK Wide 1 or Wide2 just require a mounting adapter.

https://www.eevblog.com/forum/thermal-imaging/another-project-for-fraser-fluke-lens-to-flir-camera-adapters-(exx-first)/msg1411922/#msg1411922

Fraser

[Fraser]

Something to remember when using supplemental lenses on a thermal camera...... they have an effect on both measurement calibration and IFOV.

Using a x0.5 wide angle supplemental lens increases the IFOV in proportion to the increase in FOV. This means your pixel size ‘on target’ has effectively quadrupled so you capture a quarter of the scenes fine detail at the same working distance. The inverse is true when using the Tele X2 supplemental lens, but at the cost of FOV.

Fraser

[Fraser]

The effect of a supplemental lens upon camera measurement calibration can also be significant. Much depends upon the quality of the supplemental lens. The transmission figure for the lens is needed in order to make a correction for the additional Optics introduced into the image path. It is not unusual fir a supplemental lens to have a transmission figure of around 80% so the measurement error can be significant if this is not taken into account.

Fraser

[Fraser]

Finally..... be careful when buying a Fluke lens...... not all are supplemental types. You need to ensure that it is a Wide1, Tele1, Wide2 or Tele2. Some Fluke cameras have interchangeable lens assemblies and those primary lenses are of no use to someone wanting a supplemental lens.

Fraser

[Fraser]

I almost forgot, there is extensive information on this forum regarding adding a supplemental close-up lens to a camera. You often just need to purchase a ZnSe focus lens designed fir use in CO2 laser cutter systems. These are available cheaply from China and come in different diameters and focus distances. Expect to pay around $20 for such a lens. You then mount it in front of your cameras lens by any means that suits you and your camera. Focus distances commonly range from 25mm to 100mm.

Fraser

[Jenny]

Oh my, I didn’t expect so much information, thank you so much Fraser!
Yes I did saw those posts, but those are not only too expensive for hobbyists, but they are not that universal...
What I’m asking, is the style just like you mentioned for the close-up lens — cheap, universal, and easy to get — but for changing FOV instead. Does such thing exist?
Yes, I knew that would have some drawback such as wrong temperature readings, but it would be great to be able to change FOV without changing a whole camera.

[Fraser]

Jenny,

Making a close-up lens is easy as you are basically giving a 'long sighted'thermal camera a Monocle (https://en.wikipedia.org/wiki/Monocle) for closer focus. Such is little different to us using reading glasses when long sighted and required just a single lens element. This technique is also to be found on Document cameras and presenters as they tend to use standard camera modules and lenses with a single element close-up lens in front of the objective. This is where I got the idea to use a ZnSe CO2 laser lens as a thermal camera close-up lens.... way back in my early days of thermal imaging and needing closer focus capability.

There are more sophisticated close-up lenses that use more than a single lens element. These are often described as 'microscope lenses' as they provide low distortion imaging of very small targets with ‘on target' pixel sizes of 25um or smaller. Those lenses are expensive !

OK, so to your question..... I am uncertain what you mean by universal lenses as the lenses I detailed can be mounted on many different cameras and work well. The lenses output a parallel beam as they are AFOCAL.  Making your own AFOCAL telescope is possible, as has been shown on this forum. You can construct Keplerian (inverting) telescopes with no more than two Bi-Convex of Plano-Convex lenses and such lenses are relatively common, but can be expensive. You can also construct a Galilean (non-inverting) Telescope if you can find the required bi-concave, Plano-concave or negative meniscus lens to use with a Bi-Convex, Plano-Convex or positive Meniscus lens element. Sourcing negative lenses at reasonable cost is the challenge.  Can a wide angle supplemental lens be made in a similar manner ? yes it can, but we immediately face the challenge of sourcing a suitable negative lens that is essential for such a supplemental lens. There is no wide angle supplemental simple lens design using common (cheap) positive lenses that I know of.

Will a DIY supplemental lens provide decent imaging ? Well this is no different to visible light lens assemblies. You should match the lens elements for operation together otherwise distortion, non uniformity, vignetting and focus shift across the image may result. This is ignoring the other nightmares associated with cheap visible light optics relating to wavelength differences etc. It is unlikely that a DIY supplemental lens using randomly sourced non-matched lens elements will come close to the imaging performance of a commercially produced supplemental lens that uses the correct lens profiles and powers to achieve its performance. That said, many users do not need amazing optical performance or cannot justify the related cost. For them, DIY is a clear path to follow and it becomes a great optics learning experience.   

Just consider what you are trying to achieve and why. If you have spent a significant sum on a camera, be it visible light or thermal, it makes little sense to degrade the imaging performance that you paid for by placing a crude lens assembly in front of the expensive cameras lens. If it is just an experiment or needed for a rough imaging task, then it does make sense. If you have an expensive thermal camera with decent optics, it does make sense to try to track down a used commercial supplemental lens and adapt it to your camera lens mount. You are then assured of decent optical elements configured correctly for continued good imaging.

The World is your Oyster and it really comes down to your available spare time and desire to experiment 

Fraser 

[Fraser]

A small comment on the financial aspects of DIY supplemental lenses.....

When it comes to decent quality Germanium or ZnSe lens elements bought new from known suppliers.... there appears to be no such thing as cheap, with most costing a significant sum of money.
I search for used thermal camera lenses at reasonable prices in order to obtain good quality lens elements from them at affordable prices. This is a good path to take as sellers who have extracted lens elements from used lenses tend to charge significant sums for such in the belief that the Lens element is worth its weight in germanium. Whilst Germanium does have a high salvage value, it is not the amount often quoted by sellers of such lenses. Buying used lenses is fraught with risk so be careful. You need to be certain about which thermal wavelength the lens elements are AR coated for and whether the lens is suffering age or storage related degradation. Damp conditions can corrode Germanium lens elements. And remember, most thermal camera primary lenses, used in simple configurations, do not contain negative lens elements. They are often just a Keplerian inverting telescope design.

In my experience you can easily spend more collecting together random lens elements for experimentation than you would have spent on a single, well designed commercial used lens assembly for the intended task ! With the random collection of used elements you also face the challenge of matching some up to work together and still there is the chance of poor imaging as a result.

If the total cost of the supplemental lens is a concern, I recommend against pursuing the DIY path unless you have a source of inexpensive lens elements from which to buy what you need. Making a DIY wide angle supplemental lens could end up an expensive project.

Fraser

[Fraser]

After many years of collecting thermal camera related items I still have a relatively small collection of lens elements. The reason ? I tended to buy complete lens assemblies as they often offer far better value for money and may sometimes be used without modification. My small collection of lens elements is for experiments and learning about thermal camera optics. I bought a few ZnSe CO2 laser lenses in order to achieve close-up focus capability on some of my cameras. I have the correct OEM supplemental wide, Tele and close-up lenses for my higher end cameras but they were only obtained at an affordable price after years of searching !

I have attached a picture of four storage boxes that contain a variety of lens elements and complete lens assemblies. These are for my experiments and adaption to other cameras. I might add that these are only 3 concave lenses in my collection for experimentation. They are very hard to find at hobby level prices.

Fraser

[Jenny]

Thank you very much for your suggestions Fraser.
Also, your collection is amazing!

[Fraser]

As an example of what can sometimes be found cheaply on eBay. I attach some pictures of an Inframetrics wide angle x0.5 lens.

Now this lens is pretty much useless in its current form unless you own the associated Inframetrics thermal camera as there is a lens element inside the cameras lens mount that forms part of the whole lens system. This is also to be found in some AGEMA camera designs. So why did I buy it ? Simple..... it is a LWIR and MWIR lens, stated as wide angle and it was 30 GBP ! This lens assembly contains top quality Germanium lenses coated for LWIR and MWIR broad band working, plus one of the lenses (the front one) is a negative meniscus for wide angle work  That lens element alone was worth more the the 30 GBP to me and would cost several hundred Pounds new. As an added bonus, there is a second Germanium lens element in this lens assembly so all I would need to do would be to characterise the lenses behaviour and match it into the needs of my camera, be it as a primary or supplemental lens.

Sadly such bargains are relatively rare and this is just proof of how hard I used to scour eBay looking for such items. These particular Inframetrics lenses used to be relatively inexpensive, but as people have realised how useful they can be for Germanium parts, the prices have increased significantly.

Fraser

[Fraser]

For anyone interested in the optical details of the Inframetrics 700 series cameras that use the above detailed lens, I attach the optical path diagram.

In the diagram it shows the front (objective) lens element that is mounted in the removable lens barrel. The wide angle lens that I detailed above contains two lens elements within the barrel due to the optical requirements of the design. The Collimator lens (rear lens element) is the one that is permanently mounted in the 700 series cameras body as part of the lens mount assembly. Without the Collimator lens you have only half of the intended lens assembly. This is something to be aware of if buying Inframetrics lenses. Some are complete assemblies, with all required lens elements, as they were supplemental lenses for the 500 and 600 series cameras, but the 700 series lenses are as detailed here and so less desirable to many experimenters. The Agema 450, 470, 870, 880 and 900 cameras use the same 'split lens' system.

Fraser