This lens good anything (thermal)? - Page 1
Forum section: electronics / general

author: ivaylo
author_rank: Frequent Contributor
timestamp: October 25, 2018, 11:07:23 pm
content: Found at a local liquidation place, took a picture of the label on box as well. Any information appreciated...

author: Fraser
author_rank: Super Contributor
timestamp: October 26, 2018, 12:07:25 am
content: 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 knowThe associated camera datasheet is here.....http://www.avensyssolutions.com/data_AS/File/Solutions/Mikron/MIKM7500.pdfFraser

author: ivaylo
author_rank: Frequent Contributor
timestamp: October 26, 2018, 06:34:08 am
content: 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...

author: eKretz
author_rank: Frequent Contributor
timestamp: October 26, 2018, 07:13:01 am
content: If they are LW, I will pay you for one.

author: Hydron
author_rank: Super Contributor
timestamp: October 26, 2018, 08:28:14 am
content: Quote from: ivaylo on October 26, 2018, 06:34:08 amThe 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?

author: Fraser
author_rank: Super Contributor
timestamp: October 26, 2018, 11:43:10 am
content: 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 issueI 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

author: ivaylo
author_rank: Frequent Contributor
timestamp: October 26, 2018, 03:42:39 pm
content: 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.

author: Fraser
author_rank: Super Contributor
timestamp: October 26, 2018, 06:01:11 pm
content: 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

author: ivaylo
author_rank: Frequent Contributor
timestamp: October 29, 2018, 03:54:41 am
content: 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...

author: Fraser
author_rank: Super Contributor
timestamp: October 29, 2018, 12:58:04 pm
content: 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

author: ivaylo
author_rank: Frequent Contributor
timestamp: October 29, 2018, 04:57:38 pm
content: Got it. Let me play with it some more tonight when I get home...

author: ivaylo
author_rank: Frequent Contributor
timestamp: October 30, 2018, 03:52:03 am
content: Shot a little video what the Seek Thermal see through this lens -https://youtu.be/NEwfiaPLrMUI 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).

author: Fraser
author_rank: Super Contributor
timestamp: October 30, 2018, 11:48:53 am
content: Well the tests demonstrate that the lens is not your standard supplementary type that just mounts in front of the cameras standard lensFrom 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 assemblyIn 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 thoughFraser

author: Fraser
author_rank: Super Contributor
timestamp: October 31, 2018, 03:52:00 pm
content: Ivaylo,Many thanksI will PM my details.Fraser

author: Vipitis
author_rank: Frequent Contributor
timestamp: November 01, 2018, 03:31:50 am
content: 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.

author: ivaylo
author_rank: Frequent Contributor
timestamp: November 01, 2018, 06:20:39 am
content: 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.

author: Fraser
author_rank: Super Contributor
timestamp: November 01, 2018, 11:48:45 am
content: 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 casingThe 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

author: Fraser
author_rank: Super Contributor
timestamp: November 01, 2018, 08:18:56 pm
content: 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.htmlThis may also explain the unusual objective lens profile for very close focus.Fraser

author: Hydron
author_rank: Super Contributor
timestamp: November 01, 2018, 10:43:40 pm
content: 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.

author: Fraser
author_rank: Super Contributor
timestamp: November 02, 2018, 12:40:53 am
content: 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 myselfCommercial dedicated close focus lenses are rare. If I can determine how to deploy these lenses I will add to my thermal microscope capability.Fraser

author: Fraser
author_rank: Super Contributor
timestamp: November 02, 2018, 01:35:32 am
content: 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 M7500I 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

author: ivaylo
author_rank: Frequent Contributor
timestamp: November 02, 2018, 04:19:36 am
content: 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?

author: Hydron
author_rank: Super Contributor
timestamp: November 02, 2018, 07:55:06 am
content: Quote from: Fraser on November 02, 2018, 01:35:32 amThanks 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.

author: Fraser
author_rank: Super Contributor
timestamp: November 02, 2018, 10:53:14 am
content: Ivaylo,Excellent disassemblyOK, 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 beautiesThat 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

author: Fraser
author_rank: Super Contributor
timestamp: November 02, 2018, 11:00:31 am
content: 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 useFraser

author: Vipitis
author_rank: Frequent Contributor
timestamp: November 02, 2018, 12:24:47 pm
content: Glad you were able to take it apart. Your diagram shows something like an aspherical element. Which is difficult to manufacture and design but works against distortion. 4 elements rise the value of the unit and lot; and they are also 35mm diameter so work for larger sensors.About handling them, you can use an lens assembly tool, those with a little vacuum cup or some soft pliers - or just graphics the elements on the side. I dropped my elements onto the floor and all and they survived it so far.The edge is uncoated and exposes the germanium. It's not part of the optical function for the element and usually covered in the assembly.If your elements look like a mirror in sunlight and give a green or red cast in artificial light; that's a good sign for a LW coating.Try to grab a few of those units if you can!

author: Fraser
author_rank: Super Contributor
timestamp: November 02, 2018, 01:02:07 pm
content: Eeeek .... dropping Germanium lensesThey are brittle and of a monocrystaline structure so can shatter. Chalcogenide IR Glass lenses are not as fragile in this respect. When you see a Germanium lens crystal being grown, cut, profiled on a diamond lathe and polished..... you tend to treat them like a very fine champagne glassThe AR coatings are reasonably robust if not mistreated but I have seen a lens where a user rubbed the objective to clean it after every use... he asked me how to remove the weird grey blotch that was growing out from the middle of his very expensive lens. That 'blotch' was the raw Germanium that had been exposed by excess friction on the AR coating. The AR coating was gone from the middle of the lens and I estimate around 70% area coating loss had occurred. The lens was effectively scrap in terms of its calibration profile. The owner was understandably quite sad about that.AR coatings on LW cameras can take on many appearances in different light. They sometimes look Blue, other times almost black and can appear like petrol on top of water with a lovely blue/green spectrum rainbow effect. Some have asked me to polish a lens that looked like the petrol on water effect, thinking it was some nasty surface contamination. I have been pleased to allay their fears and did not 'polish' the lenses. It is totally normal to see a sort of graduated rainbow effect on some Germanium lenses.Thankfully the OP in this thread has already tested the lens for a LW AR coating. It does pass LW but could actually be MW and LW coated as the M7500 is a multi band series of cameras. Inframetrics produced multi band coated lenses for their MW and LW scanning cameras. If at all possible, always check a lens for LW AR coatings as a MW AR coating renders the lens pretty much useless for LW working. If you can see through a lens with a LW camera, it is coated for LW. If it appears like a mirror to the camera, it is coated for something other than the LW band. Simple but not always possible when buying off eBay ! Be careful how much you risk paying on an unknown lens !Fraser

author: Fraser
author_rank: Super Contributor
timestamp: November 02, 2018, 03:48:24 pm
content: Just some pictures of the rainbow effect on thermal camera lenses.

author: ivaylo
author_rank: Frequent Contributor
timestamp: November 03, 2018, 03:21:41 am
content: Speaking of different color coatings... I did get a few more of these lenses and when I went home I noticed some of them have a different tint. One is red-ish, the other is blue-ish (I am red-greed color blind, keep in mind). Anything I've posted so far (and the three lenses I shipped to people here so far) is about the lens with the red-ish coating. I did run a quick experiment and to my untrained eye it looks like the Seek Thermal sees the same through both. Same lens structure inside. The color difference is consistent between both front and back elements. Pictures attached...

author: Hydron
author_rank: Super Contributor
timestamp: November 04, 2018, 11:26:01 am
content: I have seen quite a variation in coating colours too, even between different samples of what is nominally the same lens. The only one that seems consistent is the dark grey "Diamond like Carbon" that is often used for extra ruggedness on the front surface of an assembled lens.

author: Fraser
author_rank: Super Contributor
timestamp: November 04, 2018, 03:24:59 pm
content: Indeed, the lens colour of Fire fighting cameras is often the grey colour from the hard carbon coating.I do not know why the colour of the AR coatings varies. I assumed it was different batches of lenses and that as the coating is applied, minor differences in the process effects the colour, bit not the AR performance. As stated, some lenses have several bands of differing colours on them. This is, of course, in the visible light domain and, as we know, that means nothing in the Longwave energy domain.As a side note, Hard Carbon coatings are known as "diamond like" coatings due to their resistance to scratching. That are not indestructible though ! They should be treated with care like any optical coating.Sadly lenses that are subjected to long term damp contions can suffer degradation of their AR coatings. Hard Carbon coatings are no different. The damage is a form of corrosion and is seen as spider lined under the coating, white corrosion breaking through the coating, lifting of the coating or mottling of the coating surface. In the case of lifting, the coating can flake off in whole areas, it can rub off easily if cleaned or it becomes loose crazing all over the lens that can easily rub off if touched.Loss of the AR coating is bad news for Germanium Lenses as it directly effects the transmission of the lens. The lens will still function, but with reduced performance.Keep your lenses dry !Fraser

author: Hydron
author_rank: Super Contributor
timestamp: November 08, 2018, 01:59:17 pm
content: Mine arrived safe and sound (thanks OP!) and a _very_ quick check suggested that the lens is designed to work placed directly infront of an FPA at a back focal distance in the range of single digit to low 10s of mm. Will have a bit more info if I'm not too busy tonight (the quick check was done by simply holding the lens infront of a bare FPA so is highly unscientific - treat my initial take with a grain of salt!). Of course we don't know what magnification this is actually supposed to work optimally at, but I guess we just use it in the way it works best for our needs.

author: ivaylo
author_rank: Frequent Contributor
timestamp: November 08, 2018, 04:14:04 pm
content: Glad to hear you got it! If anyone still wants one, please PM. I got a few more when I got them for these guys. After which I may try and move them on eBay or something.

author: Vipitis
author_rank: Frequent Contributor
timestamp: November 08, 2018, 06:05:25 pm
content: I hold back on getting more lens elements arm, sorry. Can anyone with the elements give an estimate of what kind of focal length they are? My interest would be to repurpose the elements and use the rest of my collection to build a doublet refractor.

author: Fraser
author_rank: Super Contributor
timestamp: November 13, 2018, 03:26:58 pm
content: Thanks to the very kind efforts of Ivaylo, I now have two of these interesting lensesI will have a look at their characteristics as soon as possible but a few higher priority tasks must be completed first. The lenses certainly look to be very nicely made. A quality product, but sadly also quite a specialist one due to their close focus design. I have a use for such though so they are perfect for my needs.Thank you very much Ivaylo. I may just have to buy another !Fraser

author: Fraser
author_rank: Super Contributor
timestamp: November 13, 2018, 03:52:38 pm
content: I have just written to a company with direct connections with Mikron products requesting any information that they might hold on these lenses. A long shot but it is always worth asking.Fraser

author: Hydron
author_rank: Super Contributor
timestamp: November 13, 2018, 08:34:16 pm
content: Quote from: Fraser on November 13, 2018, 03:26:58 pmI'm in agreement with this and in a similar position regarding time unfortunately. The limited playing I have done with mine suggests that they work well at magnification ratios of ~0.5 with a working distance of ~4cm from the front element. With 12mm between the FPA and rear of the lens (shortest I can easily do without making a new mount - it's 44mm in diameter!) I get ~0.3x magnification and 88mm working distance. 1:1 (i.e. true macro) performance would require the target to be touching the lens (0 working distance) so is not practical. Performance looks to be better than what can be obtained with a non-close-up lens at these magnifications. Definitely good fun for the price regardless of the eventual practicality!

author: INFINIUM
author_rank: Contributor
timestamp: November 18, 2018, 10:46:25 am
content: Somebody uses the ANGENIEUX ir Lents ? , I want to transplant this F50/F1,5 From one AEG PTSi old camera to one from ALDI, use for infrared analisis in old paintings or ? chips repairs , bearings , etc.https://www.hotukdeals.com/deals/night-vision-device-9999-aldi-768263

author: Fraser
author_rank: Super Contributor
timestamp: November 18, 2018, 11:43:36 am
content: That Aldi unit is a Generation 1 image intensifier that operates in the visible and Near IR wavelengths.Your thermal camera operated in the Mediumwave Thermal band. The AEG camera is a thermal imager and is very different to an image intensifier. Your lens will not work on the Aldi device and you cannot carry out thermal imaging with the Aldi device unless the target is over around 400C when it starts to radiate NIR wavelengths.Fraser

author: Fraser
author_rank: Super Contributor
timestamp: November 22, 2018, 08:55:42 pm
content: My second pair of the close focus lenses have arrived so it is high time for me to start experimenting with themLooking at the excellent sketch of the internal lens element arrangement I am minded to remove the rear lens and see if this assembly will work as a supplimental lens with a roughly parallel beam output. Sadly life is rarely that simple though. I will report the result soonest.Now that I own four of these lens assemblies I have the opportunity to experiment moving lenses from one into another to change the characteristics. Buying such large diameter Germanium lenses and a suitable lens tube from Thorlabs would be very expensive indeed !Fraser

author: Vipitis
author_rank: Frequent Contributor
timestamp: November 23, 2018, 12:12:51 am
content: Do you see a possibility in stacking a few of these units for even closer focus?I was wondering if a laser (with a wavelength in the LWIR band) and indicator paper(the one that is thermochromatic and loses the traces when it's cooled again) would help with trail and error of lens arrangements as it makes visualization much easier.Excited for what you come up with, but I am not yet sold on getting one of these units for the pure purpose of stockpiling elements.

author: Fraser
author_rank: Super Contributor
timestamp: November 23, 2018, 12:30:44 am
content: You and I think alike on the thermochromatic film. I bought the most sensitive that I could find and have yet to play with it.Regarding closer focus. I think a small explanation of the beam path might help. I am in bed so cannot draw a pretty picture at the moment. Referring to the OP's lens cross section sketch and considering a beam entering at the left and travelling to the right......The focus point of the first lens element is the source of the 'beam'. Let's just say it is at 20mm from the front of the lens. It passes brought the first lens and exits it in a parallel beam that enters the second lens. Upon leaving the second lens the beam is refracted to the extent that it travels to the opposite side of the Third lens face. This is the point of image inversion. The Third lens receives the beam and refracts it to a roughly parallel beam again. The beam enters the fourth lens and is refracted to create a focal point at the rear of the lens where the sensor array will be located. Looking at the lens system very roughly in pictorial form, you end up with an expanding cone of beams coming from a focal point entering lens one the left, an image inversion at the mid point, and a contracting cone of beams converging to a focal point on the right after leaving lens four. The focus point of the lens would normally be set by the distance between lens two and lens three. This could possibly be adjusted for closer focus in front of the lens. Back focus distance must also be adjusted correctly.I am looking at removing lens four to see just how parallel, or not, the beams are that leave lens three. I would effectively be removing the beam convergence stage to make a three element supplimentary lens. Sods law will likely ruin this plan and require some additional beam collimation though.You would not achieve much by lens stacking in my opinion. Better to tweak the focus point of the original design.Fraser

author: Fraser
author_rank: Super Contributor
timestamp: November 23, 2018, 01:02:54 am
content: Vipitis,Regarding stockpiling lens elements..... fair comment. For the cost though, these lenses are superb. I buy cheap ZnSe elements to act as supplimentary close-up lenses. The elements within the Mikron lens would be suited to such a task as well and they are far higher quality meniscus Germanium types. So for those wanting to add a really good quality Close-up lens element to their camera, these lens assemblies may be a good source of such.The Mikron price on these close focus Mikron lenses was apparently around $5K ! Sadly I cannot source any technical specs though as Lumisense flat out ignored my RFI.FraserUpdate to post : Rough beam path Sketch added