This lens good anything (thermal)?

[ivaylo]

Found at a local liquidation place, took a picture of the label on box as well. Any information appreciated...

[Fraser]

It is a close-up supplementary lens for the Mikron M7500 Industrial thermal camera. I know that camera well. It is very versatile as it can be 'tuned' by the manufacturer to operate integrated SW, MW or LW bands with its VOX microbolometer.

It is a nice lens that I would be pleased to discover as you have. The only question is which thermal band the lens is AR coated for. If you have access to a LW thermal camera you can test it by just p,acing the lens in front of the cameras lens. If you see a good image, the lens can operate in the LW band. If little or no image appears through it, then it is coated for SW-MW and if no use at LW.

If you decide to sell it, please let me know

The associated camera datasheet is here.....

http://www.avensyssolutions.com/data_AS/File/Solutions/Mikron/MIKM7500.pdf

Fraser

[ivaylo]

Thanks for the info, google did return some of it based on the label, but I wasn’t sure what to make of that. They had a box with these. What is the material of this lens, glass, germanium, something else? The only thermal imaging thing I have is a Seek Thermal camera? Any other way to test the lense? Thx...

[eKretz]

If they are LW, I will pay you for one.

[Hydron]

Thanks for the info, google did return some of it based on the label, but I wasn’t sure what to make of that. They had a box with these. I paid $40, if there is interest and they are still around I may get a few next time I visit. What is the material of this lens, glass, germanium, something else? The only thermal imaging thing I have is a Seek Thermal camera? Any other way to test the lense? Thx...

The Seek is LWIR, and will let you check the lens coatings if you do what Fraser suggested. I'm also interested in the possibility of acquiring one, though I'd want a chance to learn more about the lens (see questions for Fraser below) and what the overall cost to get one (inc. shipping/customs) would be.

Fraser - do you have any more info as to how the supplementary lens works - I assume it is used infront of another lens of a specific focal length? What sort of working distance and magnification ratio would you get?

[Fraser]

Hydron,

The lens is supplementary, meaning it sits in front of the cameras lens. The distance is around 5mm from the camera objective but this is not critical. The cameras lens has a FOV of 21 Degrees x 16 Degrees. The supplementary lens matches into that or anything close to it. The supplementary lens is of quite large diameter so should match many thermal cameras with similar lens FOV. When placed in front of some wide FOV camera lenses, vignetting may be noticeable but the lens should still work. In a close up operation, vignetting is less of an issue

I have yet to find the specification for this particular lens. Anyone buying one does so as a calculated risk and experiment. I would certainly like one for use on my cameras. The OP can check which operating band the lenses are intended for with the Seek camera. It will be interesting to hear what he discovers. He may also be able to determine the distance in front of the supplementary lens at which focus is achieved. If adjustable, the focus of the Seek should be set for distance viewing before using the supplementary lens as this provides the best lens to lens matching.

Fraser

[ivaylo]

Thanks, Fraser for all the info! I'll see what the Seek Thermal sees through the lens (hopefully) by end of weekend and will post here.

[Fraser]

Great ! I look forward to hearing about what you find. It will also be interesting to hear where the focus point is in front of the lens. "Close focus" can be anything from tens of mm to many hundreds of mm !

Fraser

[ivaylo]

OK, this is what I did...

• The Seek Thermal I have is the CompactXR - https://www.thermal.com/compact-series.html.
• The image you are seeing is a fork I heated up on the gas stove in the kitchen.
• The titles of the images should capture what you are seeing.
• the XXX_no_lens.JPG images are straight through the Seek Thermal, no additional lens in front so you get an idea what the camera sees.
• The Seek Thermal does see through this lens so I assume it's LW.
• Unless I am missing something the minimum distance between lens and camera I could focus at is about 15cm (is it because I have the XR model camera?) so not very practical in my case to use in front of the camera. Anything closer than that is a blur, you could see light and dark areas when you move the lens around, but no detail.
• The focus of the pictures could be much better, I had trouble holding the whole setup together, focusing and taking pictures. I did play specifically with manual focus and you could achieve sharper images, but the 15cm minimum distance from camera does not change.
• The distances in cm I am listing are approximate, I do have a good sense for distance in metric, but my accuracy is probably +/- 10%.
• Because of the large distance between lens and camera I could shoot both the object and how it looks through the lens (so you can see the effect of the lens).
• I did play with direction and I *think* I got better (less distortion) images when the serrated ring of the lens is towards the camera.
• The appearance of this lens (serrated ring and all) reminded me of a microscope eyepiece so I took a few normal light pictures for comparison through the eyepiece of my microscope and they seem strikingly similar to the images from the thermal photographs. This last part is me speculating, optics isn't my strong suit, I do dabble in photography so my non-scientific instincts are from there.

Edit: Just noticed 45cm_to_object_no_lens.JPG image is flipped 180 degree, sorry about that...

[Fraser]

The lens is a sleeve mount as shown in the attached pictures of the Mikron 7500 camera that is fitted with an extended lens mount. In normal deployment it has the grip ring facing away from the camera. Reversing such a lens does produce a microscope lens effect. This is similar to the technique used by photographers who use reversed standard lenses for macro photography.

More from me on this later.

Fraser

[ivaylo]

Got it. Let me play with it some more tonight when I get home...

[ivaylo]

Shot a little video what the Seek Thermal see through this lens - https://youtu.be/NEwfiaPLrMU
I did try to bring it close to the object as well as look through both sides of the lens. Focus is fixed at about 20cm. While shooting the video could not play with focus, but all focus does when brought further is just blur everything (as it should).

[Fraser]

Well the tests demonstrate that the lens is not your standard supplementary type that just mounts in front of the cameras standard lens

From what I have seen, this lens assembly is designed to be installed in a sleeve mount that has another lens element within it. That is to say, this lens assembly is missing its rear lens element that resides in the mount assembly

In order to use this lens with a camera I believe that some experimentation would be needed with placing a lens between it and the camera lens. There is also the very real possibility that this is a primary lens assembly and thus would illuminate the microbolometer via another (fixed) lens.

In either case I regret to advise that this us very much an experimenters lens and not a 'turn key' solution for close up imaging.

I am still interested in buying a couple of these lenses for experimentation though

Fraser

[Fraser]

Ivaylo,

Many thanks 

I will PM my details.

Fraser

[Vipitis]

can you or someone who got them second hand figure out how many lens elements and what specs they are? I would be interested in more elements if they have a good diameter and are meniscus for example.

[ivaylo]

I did look into taking it apart, but for the 5 minutes I looked I didn’t see how to do it in a nondestructive way. There are holes at 180 deg of each other on one end, but where I expected to see bolts there is nothing. I’ll scratch some more to see if they are not potted or something. I’ll probably cut it open, but only after I figure out I can’t use it for anything else.

[Fraser]

These lenses tend to use fine threads on the end(s) and a varnish type glue to lock them. They can be very hard to dismantle without a lot of torque and scratches to the casing

The finger hold end likely unscrews from the barrel so it may be possible to see the join line between the barrel and finger hold piece. This join is not always where you would expect ! It can be in the rear edge of the finger hold as the end cap can be just that.... a hollow cap, rather than a solid screw in 'plug' assembly.

I would expect the lens to be a reverse Keplerian telescope so it would contain just two lens elements and would be inverting. Note that The front lens element is an unusual profile and not your common meniscus type. It is similar to that used by NEC AVIO.

Fraser

[Fraser]

Some light research on these lenses suggest that they are part of a thermal microscope system.

This lens assembly would mount in a long lens extension tube a little like the one in the attached picture.

This is the reason why the lens assembly needs to be some distance from the SEEK camera.

Janos produce the ASIO thermal microscope range that I believe to be similar.

https://www.janostech.com/products-services/thermal-imaging-lenses/asio-lenses.html

This may also explain the unusual objective lens profile for very close focus.

Fraser

[Hydron]

So you think this is designed to "illuminate" the FPA directly, without an additional lens in the way, but at a fairly long extension? Would be good news if that were the case, as bridging up an extension tube is a lot easier than finding another mystery lens to match with.
I'd be keen to get one if so, would be nice to use a lens designed for good performance at close distance rather than unscrewing an infinity optimised lens as far as possible. If it made shipping easier/cheaper it may also be worth looking into combining shipping for a few people in the UK if the OP succeeds in getting more.

[Fraser]

I regret the exact lens design and its deployment requirements are still unknown. There could be another lens, or more than one lens in the path to the FPA. Sadly Mikron do not list such a thermal microscope or even availability of specialist lenses for the M7500. It could be a custom lens contract for industry.

I will know more when I have the lenses for testing. In the mean time I can check some of my other lenses to see how they behave. The large exit 'pupil' suggests to me that this lens works into another lens but I may be wrong. These are unusual lenses and I did not hesitate in ordering a couple as result. I have learnt that when an unusual lens becomes available at a reasonable cost, buy it, as such may not become available again any time soon. I am a thermal imaging experimenter though so can justify the cost to myself  Commercial dedicated close focus lenses are rare. If I can determine how to deploy these lenses I will add to my thermal microscope capability.

Fraser

[Fraser]

I spent a few more seconds thinking about the M7500 camera and this lens that is apparently intended for use with it.

What do I know about the M7500 camera with respect to the lens ?

The M7500 incorporates a non removable lens block that provides a 21 x 16 Degree FOV.
At least two supplimentary lenses are available for the M7500. Both mount on the front of the M7500
I can find no mention of a M7500 fitted with a different FOV primary lens.

I now strongly suspect that the lens that forms the subject of this thread, is indeed a supplementary close focus lens, but we just do not have all the parts that were used to deploy it !

It would appear that a supplementary lens mount kit was available for the M7500 and this provided a sleeve mounting on the camera front bulkhead. In theory, the close focus lens would be mounted onto the M7500 using a combination of the sleeve mount adapter and an extension tube of some 200mm or so length. Would the 21 x 16 Degree FOV primary lens match into such an extension and lens combination ? Well if we use the 21 Degree HFOV figure and consider 150mm to be the distance from the primary objective lens to the rear of the supplementary lens...... simple trigonometry suggests that the exit pupil of the supplementary lens would need to be around 55mm diameter. Not a million miles away from what is likely to be present on the lens in question.

Of course this is real 'Bush Optics' and in no way accurate as we do not know enough about the supplementary lens and its output beam characteristics. I could be way off with my crude assumptions. It could be that a beam collimation lens stage is used between the supplementary lens and the cameras primary objective. I really do not know for sure.

The fact that an image may clearly be viewed through the mystery "supplemental" lens is good news but we must remember that the lens assembly appears to be inverting. Some cameras can correct this optical inversion 'on camera' whilst others require the operator to correct the X and Y inversions via post capture software. I have met this inversion issue with other supplementary lenses as it makes their manufacture cheaper with less lens elements required. This also provides less path attenuation. The scene inversion issue is dealt with easily in software.

I look forward to experimenting with these lenses. Sadly cameras with wide angle lenses will suffer vignetting issues, is some cases such as with 40 Degree HFOV lenses, the vignetting will be significant causing a loss of usable resolution. My industrial cameras tend to use 24 Degree HFOV lenses so are still a pretty good match and they have excellent focus range for fine tuning purposes.

Fraser

[ivaylo]

OK, I wasn't trying hard enough. It opened relatively easy actually, just like Fraser said the top unscrews. It has four elements, attaching a crude diagram as well. The elements' material is interesting the edges are either metalized or could this be germanium or something (pictures of that too). Fraser mentioned that it could be Germanium or Chalcogenide IR glass. Whatever it is how do I treat it? Can this be wiped, cleaned, touched? Or is it some super sensitive coating which disappears when you breathe on it?

[Hydron]

I spent a few more seconds thinking about the M7500 camera and this lens that is apparently intended for use with it.

What do I know about the M7500 camera with respect to the lens ?

The M7500 incorporates a non removable lens block that provides a 21 x 16 Degree FOV.
At least two supplimentary lenses are available for the M7500. Both mount on the front of the M7500
I can find no mention of a M7500 fitted with a different FOV primary lens.

I now strongly suspect that the lens that forms the subject of this thread, is indeed a supplementary close focus lens, but we just do not have all the parts that were used to deploy it !

It would appear that a supplementary lens mount kit was available for the M7500 and this provided a sleeve mounting on the camera front bulkhead. In theory, the close focus lens would be mounted onto the M7500 using a combination of the sleeve mount adapter and an extension tube of some 200mm or so length. Would the 21 x 16 Degree FOV primary lens match into such an extension and lens combination ? Well if we use the 21 Degree HFOV figure and consider 150mm to be the distance from the primary objective lens to the rear of the supplementary lens...... simple trigonometry suggests that the exit pupil of the supplementary lens would need to be around 55mm diameter. Not a million miles away from what is likely to be present on the lens in question.

Of course this is real 'Bush Optics' and in no way accurate as we do not know enough about the supplementary lens and its output beam characteristics. I could be way off with my crude assumptions. It could be that a beam collimation lens stage is used between the supplementary lens and the cameras primary objective. I really do not know for sure.

The fact that an image may clearly be viewed through the mystery "supplemental" lens is good news but we must remember that the lens assembly appears to be inverting. Some cameras can correct this optical inversion 'on camera' whilst others require the operator to correct the X and Y inversions via post capture software. I have met this inversion issue with other supplementary lenses as it makes their manufacture cheaper with less lens elements required. This also provides less path attenuation. The scene inversion issue is dealt with easily in software.

I look forward to experimenting with these lenses. Sadly cameras with wide angle lenses will suffer vignetting issues, is some cases such as with 40 Degree HFOV lenses, the vignetting will be significant causing a loss of usable resolution. My industrial cameras tend to use 24 Degree HFOV lenses so are still a pretty good match and they have excellent focus range for fine tuning purposes.

Fraser

Thanks for the explanation, despite the lack of any certainty I think I'll have to bite too (if any are still available) given the potential fun playing around with one. I have a few lenses (and some loose elements) available to play around with to try and cobble something together with, along with the ability to flip images electronically, so hopefully can make something work.

[Fraser]

Ivaylo,

Excellent disassembly 

OK, what we have here is a high quality, low distortion lens structure that uses four Germanium lenses. The metal edge is typical of such. Those lens elements are real beauties  That lens assembly would normally cost several thousand Dollars from the OEM.

That front lens element is a very clever profile to meet the needs of a low distortion close focus lens.

Regarding how to handle the lens elements......

The objective is usuall coated with a pretty robust AR coating, sometimes this is a hard carbon coating. The other lens elements also have an AR coating but it is often more fragile and liable to damage if treated roughly or exposed to moisture or humidity for a prolonged period of time.

I suggest not cleaning them with anything except compressed air unless there is a finger print on them, or similar. A dry microfibre spectacles cloth may be gently used on them and a very soft cloth dampened with IPA is also acceptable. Just do not rub with a rough cloth, tissue or with undue force. Treat like a quality coated SLR camera lens and you will be OK.

Fraser

[Fraser]

Take a look at the Edmund Optics paper to be found here ......

https://www.edmundoptics.com.au/resources/application-notes/microscopy/understanding-microscopes-and-objectives/

Look at figure 8 onwards. Look familiar ?   

This document may help us better understand this lens and its use 

Fraser