Germanium or ZnSe lens for DIY hobbiyist projects... - Page 1
Forum section: electronics / general

author: Lambda
author_rank: Regular Contributor
timestamp: March 22, 2021, 09:32:04 am
content: Hello.I was asking myself the following thing:- We can use for our LWIR imager Germanium lens or ZnSe lens (just the two most common materials, not exhaustive disclosure).But when i consider for instance this document:https://www.laseroptik.de/en/substrates/standard-substrates/si-znse-and-geWhy not, if there is no specific hardness requirement, choosing systematically ZnSe material offering a higher transmission (in the range of 8um-14um), while being cheaper than Germanium equivalent lens?I read some thread here dealing with this subject (ZnSe vs Ge), but it is still not obvious for me to understand the manner to select properly the good material for an imager.Shortly said, for a normal using in normal domestic/outdoor conditions for a hobbyist, would it not be simply the best choice to select systematically the ZnSe material instead of Germanium one ?Thank you in advance for your lights on this subject.Best regards.Stéphane

author: Ultrapurple
author_rank: Super Contributor
timestamp: March 22, 2021, 11:41:07 am
content: Or indeed evenKRS5 Thallium Bromo-Iodide, which is good from visible red down to around 30µm, or possibly evenAMTIR, though it's only OK to about 13 or 14µm.This page on IR materialsmakes interesting reading. I wasn't aware that gallium arsenide was a good, tough IR material.

author: Vipitis
author_rank: Frequent Contributor
timestamp: March 22, 2021, 12:15:28 pm
content: Germaium has the highest refractive index. Meaning you can built much more compact lenses. It does need to be coated tho, which will add to the cost.ZnSe isn't opaque to the visible spectrum, so you can kinda see what you are doing.

author: Fraser
author_rank: Super Contributor
timestamp: March 22, 2021, 12:27:43 pm
content: I have Germanium, Chalcogenide IR Glass, ZnSe and GaAs lenses in my inventory.Professional lenses used in very expensive thermal imaging systems use either Germanium or a combination of Germanium and ZnSe in the optical block. ZnSe is an excellent performer over a large range of wavelengths.With regard to cost, Germanium is often seen as a very expensive lens option but I can tell you that a high performance ZnSe lens can easily cost as much, sometimes more that a Germanium lens of the same physical dimensions. The manufacturing process and accuracy of the finished lens dictates its cost to the end user.People may think that ZnSe lenses are very inexpensive because you can buy decent 20mm diameter lenses for around $30 on eBay. Try looking for a 30mm or larger ZnSe lens though. You will see that he prices rise significantly when you move above 20mm diameter. The reason for this is that the smaller diameter ZnSe lenses are mass produced for the budget CO2 laser cutter and engraver markets. Those lenses are not intended to be used for any imaging application and their data sheets advise this. They are fine for CO2 laser work and non demanding imaging applications but are not in the same league as a ZnSe lens made for imaging applications. It is all about surface quality and tolerances. We get away with cheap ZnSe lenses for close-up supplemental lenses because we can tolerate the distortion and any other optical anomalies in that scenario. It comes down to the performance desired from the lens in a particular application.Gallium Arsenide is also used for lenses in CO2 laser systems but is less common. It is a harder, more durable, material but it suffers from the same ‘built to a cost’ limitations of budget ZnSe CO2 laser lenses so is not normally recommended for imaging applications. I have used a 20mm diameter GaAs lens as a close-up supplemental lens and it works well in that application.When thinking of building a complete lens block to mount in front of a microbolometer array, you have to consider cost. Mass produced lens blocks for thermal imaging are not inexpensive but if you try to make your own you may be surprised at how expensive each high quality lens element will be and you need to have an excellent understanding of optics to match the various lens elements to each other in order to produce a good result. It is often cheaper to buy a commercial lens from the likes of Ophir. The lens will be made with Germanium elements (more expensive), Chalcogenide IR transmissible glass (less expensive but still not ‘cheap’) or a hybrid that also uses ZnSe in the lens design.Chalcogenide IR transmissible glass has revolutionised the production of lower cost lens blocks for thermal imaging systems. The production process is completely different to that of Germanium and even ZnSe lenses as the lens element is moulded in a special high temperature autoclave device. The performance of these moulded lenses has improved over the years and they are common in lower cost thermal imaging systems.Hope this helpsFraser

author: Fraser
author_rank: Super Contributor
timestamp: March 22, 2021, 12:35:47 pm
content: I should also say that I buy used thermal imaging lenses and either use them ‘as supplied’ or adapt them to my needs. This is far less expensive than buying a new lens or even making my own using individually purchased elements.Fraser

author: Fraser
author_rank: Super Contributor
timestamp: March 22, 2021, 01:06:46 pm
content: As stated by Vipitis,Refractive Index:BK7 (Crown) optical glass = 1.51 (visible light - only for reference)Germanium = 4.00 at 11umZnSe = 2.40 at 10.6umGaAs = 3.27 at 10.3umChalcogenide IR glass = 2.49 @ 10.0um (Umicore GASIR1)When working with Germanium lens elements, some lens design simulators are not able to cope with a refractive index as high as 4.00 so I use a RI of 2.0 and half the calculated distances between lens elements when experimenting with the design.

author: Fraser
author_rank: Super Contributor
timestamp: March 22, 2021, 01:56:25 pm
content: I realise that we have not really stated why a particular lens element material is chosen for use in a thermal imaging system. My thoughts on this selection process by the designer are as follows, but I am not a lens designer so this list is potentially incomplete/incorrect, though logical to me.1. Cost, Cost, Cost ! Cost of parts on a BoM can be a high priority for a design team.2. Imaging performance of the material, including properties such as ambient temperature sensitivity. Temperature effects sometimes require lens element temperature measurement in a final camera design.3. Material robustness and resistance to damage/scratching. Special protection layers are sometimes added. Unprotected ZnSe is easily scratched as it is a relatively soft material.4. Required dimensions and weight of lens assembly (Refractive Index plays a part if thin lenses are required) More lens material can also mean higher production cost.5. Transmission loss (not as important as some may think but decent transmission figures are required)6. Ease of manufacture and lead times after order7. Any special handling or specific design requirements dictated by a particular material (can impact design costs and even production line handling)8. Inherent Optical performance limitations of a material and its effect, if any, on the desired iimaging performance. (GASIR is a compromise material and inferior to Germanium in imaging performance) This may seem like a repetition of entry 2. on this list but it relates to the OEM’s tolerance for less than perfect optical performance. A designer can build a ‘Gold Standard’ solution but the OEM may prefer a ‘Silver’ or ‘Bronze’ standard solution to meet BoM cost targets and market position of the end device. Any production savings mean more profitIt is not unusual for a design team to meet their goals only for the management team to move the project ‘goal posts’ and request a cost-benefit analysis to reduce cost. The lens in a thermal camera is an expensive element of ten design so coat cutting measures may be employed to make economies. Such may be tolerable in the end products performance however. An example of this approach is the FLIR Lepton with its less than ideal LWIR Silicon Diffractive lens !

author: Bill W
author_rank: Super Contributor
timestamp: March 22, 2021, 02:40:33 pm
content: Quote from: Lambda on March 22, 2021, 09:32:04 amDispersion has to be considered (refractive index vs wavelength) where different wavelengths focus at different distances for a simple lens.http://www.reading.ac.uk/ir-infraredmaterials-znse.aspxA ZnSe element is often used to correct the effects of Ge lensesBill

author: Lambda
author_rank: Regular Contributor
timestamp: March 22, 2021, 02:43:59 pm
content: Thank you to everybody for, again, this massive amount of good informations!Shortly said:i am considering to "upgrade" the genuine optics of my little Indigos A10 core (right now: ZnSe Lens 8mm/1.2) and i am simply looking for an reasonable affordable replacement having the following features (focal length around 20mm, and F/D <=1). And in my quest i took also into consideration that i do not need a specific optimized compacity and also i am not exposing to harsch industrial or climate conditions my camera, generally speaking.Working with a low resolution core (160x120) and being interested for the specific use of my core in a general handheld night vision spotter, adapted to walk with, i am looking in a good compromise budget/performance.This is why i was trying to enlarge my scope of investigation with, to be honest, a main concern about price, indeed....In this sense, i noticed that's it can be found some lens in the second hand market, which would be fine for my using....Some example from E-Bay....https://www.ebay.com/itm/Fluke-Lens-20mm-Ti-45-Thermal-Camera-Lens-JTI-40328-1192/123707505125?_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20160908105057%26meid%3D0ad17537cc604c08a5f1e460704633c0%26pid%3D100675%26rk%3D4%26rkt%3D15%26mehot%3Dnone%26sd%3D123869965063%26itm%3D123707505125%26pmt%3D0%26noa%3D1%26pg%3D2380057%26brand%3DFluke&_trksid=p2380057.c100675.m4236&_trkparms=pageci%3Ad58d9bae-8b1a-11eb-a628-22195132796c%7Cparentrq%3A5a5611521780a69d5666c1e9ffbf6421%7Ciid%3A1https://www.ebay.com/itm/Fluke-10-5mm-Thermal-Camera-Lens-for-TI-45-TI-55/123869965063?_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20160908105057%26meid%3D0ad17537cc604c08a5f1e460704633c0%26pid%3D100675%26rk%3D1%26rkt%3D15%26mehot%3Dnone%26sd%3D123869965063%26itm%3D123869965063%26pmt%3D0%26noa%3D1%26pg%3D2380057&_trksid=p2380057.c100675.m4236&_trkparms=pageci%3Ad58d9bae-8b1a-11eb-a628-22195132796c%7Cparentrq%3A5a5611521780a69d5666c1e9ffbf6421%7Ciid%3A1ZnSe or Germanium soultion.... among other propositions....But still, this is not loaf of bread price, and i can understand that.I was also taking a look to the ZnSe lens used for CO2 laser engraver, but what i have seen is that their F/D is not very fast (i saw nothing in this range of <=1).What i consider quite important for me is:- F/D as low as possible (<=1)- a good transmission in the 8.14 um rangeThe stability in temperature would be less critical because i am not using a high resolution core and i am in a quite general using with not precisely monitoring or making radiometry of a specific target. Just increasing the general sensitivity of my system and trying to decrease its real NETD would be a good achievement for me.Thank you for your input. i have to keep on studying that closer.Best regards.Stéphane

author: Fraser
author_rank: Super Contributor
timestamp: March 22, 2021, 02:59:00 pm
content: F1.2 is a common lens speed in thermal imaging. F1.0 is also commonly found but less than 1.0 is less common these days. Do consider the effect of small F numbers on depth of field as you could end up having to refocus your camera a lot !Also consider the imaging sensor dimensions of your camera when looking at used lenses. Older lenses may be designed for larger sensor dies so the FOV will be smaller than found in the lenses original deployment.The Omega/A10 was never a particularly high performance core as it was intended to be a very versatile compact unit, rather than offering amazing low noise levels etc. You may end up spending a lot of money for not much gain with that core. Better to save your money and buy a Used TAU2 when you find one at a decent price.Fraser

author: Lambda
author_rank: Regular Contributor
timestamp: March 22, 2021, 03:24:13 pm
content: Quote from: Fraser on March 22, 2021, 02:59:00 pmFraser, this is really speaking to me. I have exactly regularly the same concerns to be careful about for my DIY night vision projects used for astronomy/terrestrial spotting, because using some lens a bit exotic/vintage....I will follow your advice and keeping on investigating on a core like the TAU 2 as you indicated to me....Nevertheless, soon, i will have to contact Bill (in advance thank you Bill) because i saw also a reasonable alternative (Argus 2 or 3 lens) to play with here (just to check indeed the provided image circle provided by these lenses).http://www.fire-tics.co.uk/spares.htmI think i will not invest more in this sense, for the A10 core, as you advised me.Stéphane

author: Fraser
author_rank: Super Contributor
timestamp: March 22, 2021, 03:26:19 pm
content: I have a brand new example of the lens you referenced in my inventory so I just dug it out to show you how large it is !It is a very nice quality lens but it is as large as you Omega/A10 cameraThe rear aperture is huge and would over illuminate your microbolometer die.If you really want one I will sell it but I would not normally recommend such a lens on an A10.Fraser

author: Fraser
author_rank: Super Contributor
timestamp: March 22, 2021, 03:28:03 pm
content: The Argus 2 and 3 lenses from Bill are a bargainFraser

author: Lambda
author_rank: Regular Contributor
timestamp: March 22, 2021, 04:01:54 pm
content: Quote from: Fraser on March 22, 2021, 03:26:19 pmThank you for these instructive photos! I keep it in my dedicated folder!Quote from: Fraser on March 22, 2021, 03:26:19 pmIf there is no specific compacity and large FOV requirements, in a (thermal) project, on one hand the image circle would not be fully used, with a too small sensor, indeed, but on the other hand, the best area, close to the optical axis of the lens, would be used, with less geometrical aberrations and "chromatic" dispersion, would not be?For my NV projects, this is my tendancies... to have an over sized image circle and just using the central part of it, for a given size of my sensor (CCD or CMOS, or photocathode from image intensifier), especially when using fast "touchy" optics (Litton 50mm/0.7, De Oude Delft 90mm/1.0, and so on....) in order to have the best image i can.Depth of Field would be indeed tricky to manage, but not a big issue for me, just indeed a bit cumbersome on the ergonomic point of view.Thank you for your potential offer, i keep it in mind for future, we never know!Stéphane

author: mawyatt
author_rank: Super Contributor
timestamp: March 22, 2021, 05:45:30 pm
content: Fun story related to ZnSe and Ge optics. Back in ~1980 we were developing an important instrument to give early battlefield warning of a chemical attack and relied on passive spectral radiometry at a distance. This instrument was later called the XM21 and worked in the 8-12 micron region and employed all ZnSe optics as dictated by the optical physics purest. The instrument was to used by solders in the battlefield and required passing the classic military EM Compatibility tests in addition to the EM pulse from a point blank thermo-nuclear detonation (crazy but a customer requirement!).So the EMC folks required the optical input lens to be covered with a dense wire mess to pass these tests, basically causing an additional ~20% optical thru put loss. After an enormous amount of engineering had gone into getting the instrument sensitive enough to "see" the atmospheric details at up to 5 miles and doing so completely passively, this didn't seem like a good approach! We staring looking for an alternative and came up with Ge as a possibility, however the optical purest insisted on the ZnSe for all the optical components. After some serious discussion and challenges we got the the optical purest to evaluate a Ge lens for just the instrument front, and use ZnSe everywhere else. We devised a blind A/B lab test which showed both as having the same response with no real difference in performance. This was a rather large rectangular lens about 160mm by 80mm I recall and thick to pass the wavefront explosive force for the thermo-nuclear blast wave.However we still had the EMC to pass, and these folks insisted on the wire mess approach which would have the same effect in reducing the sensitivity. The ace up our sleeve was doping the Ge lens to increase the conductivity to a level where the lens would act as a 3D transmission medium from free space to the front lens side and from the lens to free space on the interior side, so in effect just the opposite of an anti-reflective coating but a highly reflective on both sides at the frequencies of the EMC test and EM pulse. Straight forward transmission line theory was applied to show the attenuation caused by the doped Ge lens was sufficient to pass all the tests. Needless to say the EMC and optical purest were highly skeptical and so another series of lab tests were established to confirm EMC compatibility and verify the 8-12 micron thru put wasn't significantly affected. This worked and the instrument passed all the EMC conducted and radiated tests, including the ridiculous EM pulse and blast wave tests. This was a fun project that went on to full production and help provide early warning for solders of impinging chemical attacks when deployed.Best,

author: Fraser
author_rank: Super Contributor
timestamp: March 22, 2021, 06:56:22 pm
content: mawyatt,That is a great piece of historyJust like the ‘right tool for the job’ the right material for the application is important ! Interestingly I was thinking that the purist might have elected to go ‘all Germanium’ as it that was “what everyone uses in high performance MWIR and LWIR imaging systems”. On paper, Germanium certainly has its ‘issues’ but these were tolerated due to the benefits that offset them. ZnS and ZnSe are certainly excellent performers but have their own issues.Scientific ‘purists’ can be a great asset but I always thought it good to pair them up with someone who has a healthy dose of common sense and real life experience in the applicable field of development. Just like with many projects, there are often several teams contributing to achieve the desired end result and the art is to get them all playing nicely together and leaving their Ego’s at the doorI suspect NASA and the ESA are prime examples of superb co-operative working to overcome hurdles and achieve the desired result to everyone’s benefit.Fraser

author: bap2703
author_rank: Regular Contributor
timestamp: March 22, 2021, 07:26:55 pm
content: Is it this guy ?Most photos of it show only its backsideGrabbed here :https://www.semanticscholar.org/paper/CHEMICAL-DEFENSE-EQUIPMENT-O%27Hern-Dashiell/07889ce00d201692bc171aaee1c5914d9cbc145e/figure/22

author: mawyatt
author_rank: Super Contributor
timestamp: March 22, 2021, 08:39:17 pm
content: Quote from: bap2703 on March 22, 2021, 07:26:55 pmYes, that's the M21, good find!! The XM21 version was the development instrument. The input "window" is smaller than I recall, but this was ~40 years ago, so my memory isn't that goodhttps://www.google.com/imgres?imgurl=https%3A%2F%2Ffas.org%2Fman%2Fdod-101%2Fsys%2Fland%2Fm21.jpg&imgrefurl=https%3A%2F%2Ffas.org%2Fman%2Fdod-101%2Fsys%2Fland%2Fm21.htm&tbnid=EtCHDYIV3hbI3M&vet=12ahUKEwi5iM7y4cTvAhWB8FMKHWhbA5gQMygAegQIARAu..i&docid=95T54_HNFVHr6M&w=450&h=574&q=XM-21%20Chemical%20Agent%20Detector%20Newsweek%20cover&client=safari&ved=2ahUKEwi5iM7y4cTvAhWB8FMKHWhbA5gQMygAegQIARAuhttps://www.google.com/url?sa=i&url=https%3A%2F%2Ffas.org%2Fman%2Fdod-101%2Fsys%2Fland%2Fm21.htm&psig=AOvVaw0ine2RL2vJhY-JpaC9keAL&ust=1616532210377000&source=images&cd=vfe&ved=0CAMQjB1qFwoTCMiQp_PhxO8CFQAAAAAdAAAAABAIThe XM21 contained a small moving mirror interferometer that was servo locked to a HeNe laser by means of interference counting the HeNe wavelength, which coherently clocked the 18 bit ADC. This proved very effective technique in reducing vibration effects, including those from the internal 70K Sterling Cycle Cooler. Also had a good reference blackbody (Stefan-Boltzmanns Blackbody approximation) that could be servoed to various temperatures and included a special "reference molecular" signature plastic film, all for self calibration. Nothing moved externally, the scanning was done with a stepper motor controlled moving a diamond turned aluminum mirror. It was easy to use, just mount on the tripod and plug in power, that was it unless the scan field needed changing which was also easy.The mentioned nuclear effects caused a big increase in cost, which was a good example of poor value engineering IMO.Best,

author: Bill W
author_rank: Super Contributor
timestamp: March 22, 2021, 10:24:41 pm
content: Quote from: Lambda on March 22, 2021, 04:01:54 pmGenerally yes for all the geometric issues of off-axis and spherical, but 17u pixels and a lens of 15mm / f/1.0 is not much depth of field, a small aperture loss may be worth it.Bill

author: mawyatt
author_rank: Super Contributor
timestamp: March 22, 2021, 10:41:45 pm
content: Quote from: Fraser on March 22, 2021, 06:56:22 pmFraser,Thanks. A part of the story I didn't mention was during the test for the Congressional Staffers (US Pres. Regan's science advisor wanted to shut the program down, saying it was impossible to passively detect the agents at distance without illumination, thus a demo test was setup) one of the staffers was suspicious of the test instrument tracking a jeep spraying the chemical agent simulant a few miles away. The test instrument had a head unit and was run by Honeywell Level 6 minicomputer inside a Winnebago that had the generator running to power the minicomputer & test. A large cable ran from the Level 6 to the instrument tripod mounted the head unit which contained the interferometer, HgCdTe detector and cooler, and the support electronics. An operator was manning the Level 6 inside the Winnebago which was running the system software. The very clever staffer was suspicious that this person was pushing buttons inside the Winnebago causing the sector lights on the head unit to track the jeep, and the instrument wasn't actually detecting and tracking the sprayed simulant.While no-one was looking he took off his coat and placed it over the head unit blinding the instrument, and the sector lights began to go off. After being discovered he removed the coat and the instrument began tracking the simulant again. This immediately sold the program to all the staffers and other government folks witnessing the test!!!Best,

author: bap2703
author_rank: Regular Contributor
timestamp: March 22, 2021, 10:55:37 pm
content: Nice storyHopefully no one noticed that the simulant was refrigerated.Just kidding

author: mawyatt
author_rank: Super Contributor
timestamp: March 22, 2021, 11:23:49 pm
content: That's funny!! Could have heated it tooAnother part of this story involves the HgCdTe detectors that Honeywell produced back then, they were the most sensitive available from anywhere. In fact, they actually had Qe better than the accepted theory at the time. These were used by many other companies and also used on a program to track and destroy incoming ICBMs using a tracking sensor on the interceptor missile to spot and track the ICMB in space. A US Air Force General asked a colleague to describe the sensitivity of these HgCdTe detectors in laymen terms, he came up with "Detecting the heat of a human body at 1000 miles!". This quote eventually ended up in Tom Clancy's Cardinal of the Kremlin book, which Tom got from the General's address to Congress about the program called "The Homing Overlay Experiment".Lots of fun topics from back thenBest

author: mawyatt
author_rank: Super Contributor
timestamp: March 23, 2021, 11:23:24 am
content: Quote from: Fraser on March 22, 2021, 06:56:22 pmFraser,Should mention the "we", was 3....me, myself and I!! The Physics "Purists" were 5 or 6, with entire careers, PhDs, and post doc in this field, the EMC folks were the entire department!! So this was not an easy endeavor, convincing all these folks of a different path forward. However, "we" were very stubborn and persistent and eventually it paid offBest,

author: Fraser
author_rank: Super Contributor
timestamp: March 23, 2021, 12:30:15 pm
content: Well done for being both stubborn and persistent but I suspect you also possess a healthy dose of diplomacy in your dealings with other peopleI am pleased that you were shown to be correct in your views and maybe the other teams learnt a valuable lesson...... to be open minded and to sometimes think outside the box !

author: Lambda
author_rank: Regular Contributor
timestamp: March 25, 2021, 10:23:46 am
content: Hello again,Sorry, i am coming bothering you again on this subject, but only because as a new born in this field i try to build my culture on it...While investigating on cheap possibilities for LWIR optics, i was of course digging in this ZnSe lens for CO2 engraver laser.I know, from your teaching, that these cheap lenses are nice to use for testing some concept, but are not optimized for imaging applications.Nevertheless, i found something like that, which are interesting for me (F/D around 1 available, 25mm focal length, for instance)...https://www.ebay.com/itm/II-VI-CVD-Znse-GaAS-Focus-Lens-for-CO2-Laser-12-15-18-19-20-25mm-FL-1-4/332449376632?_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20160908105057%26meid%3D70cf8b002f924d4bb3eb36d71d045977%26pid%3D100675%26rk%3D2%26rkt%3D15%26mehot%3Dnone%26sd%3D321078811086%26itm%3D332449376632%26pmt%3D0%26noa%3D1%26pg%3D2380057&_trksid=p2380057.c100675.m4236&_trkparms=pageci%3A13a95051-8d52-11eb-8cc4-129e13dfe8ce%7Cparentrq%3A68db8c8a1780aaf48975e176ffce72b2%7Ciid%3A1But for me it is not clear what is the difference between a "ZnSe" lens and a "II-VI ZnSe lens" ?I guess also that the surface state with lambda<2 is not the usual minimum lambda<4 parameter required for meeting the diffraction limited conditions.But at the end, do you think that nevertheless, this lens would be a good candidate for general imaging application (landscape monitoring, night vision spotter hand held with low magnification, for night walking, and used with a low resolution core 160x120)?Thank you for your lights.Best regards.Stéphane

author: Vipitis
author_rank: Frequent Contributor
timestamp: March 25, 2021, 11:16:05 am
content: A single lens element doesn't make a useable lens. The best you probably get is close focus.Your best chance is to get one from Bill and please handle with more care than me.

author: Bill W
author_rank: Super Contributor
timestamp: March 25, 2021, 03:56:43 pm
content: Quote from: Lambda on March 25, 2021, 10:23:46 amII-VI might simply be a reference to the periodic table.I'd be more concerned that someone who cannot spell 'focus' is capable of anything more than copying a lens specification from somewhere else and the actual parts could be quite different.An otherwise perfect single spherical element would still exhibit all the classical spherical aberrations if used for imaging.https://en.wikipedia.org/wiki/Spherical_aberrationBill

author: Lambda
author_rank: Regular Contributor
timestamp: March 25, 2021, 04:15:48 pm
content: Quote from: Bill W on March 25, 2021, 03:56:43 pmOk Bill. indeed you right:https://en.wikipedia.org/wiki/Zinc_selenide"ZnSe can be made in both hexagonal (wurtzite) and cubic (zincblende) crystal structure.It is a wide-bandgap semiconductor of the II-VI semiconductor group(since zinc and selenium belong to the 12th and 16th groups of the periodic table, respectively)."Quote from: Bill W on March 25, 2021, 03:56:43 pmMy bad, i was copying by hand under Paint the title from this announce....typo mistake in my hurry to post between two job tasks....Stéphane

author: Fraser
author_rank: Super Contributor
timestamp: March 25, 2021, 05:54:41 pm
content: II-VI Incorporated are a lens manufacturing company. I have some of their lenses.Sadly the usual risks of fakes apply to eBay purchases.https://ii-vi.com/optics/Edmund Optics are an agent fir II-VIhttps://www.edmundoptics.co.uk/company/brands/ii-vi/CVD (Chemical Vapour Deposition) lenses are the better quality or “Hi-Q” CO2 lenses but remain a laser beam manipulation lens rather than being intended for high quality imaging.Fraser

author: Lambda
author_rank: Regular Contributor
timestamp: March 25, 2021, 06:25:06 pm
content: Thank you Fraser.Indeed, the fake aspect is sadly obvious, when looking closer at your references and the E Bay offers...An other example from Thorlabs.https://www.thorlabs.com/thorproduct.cfm?partnumber=LA7542-E3to compare to the offer from E-Bay:https://www.ebay.com/itm/II-VI-CVD-Znse-GaAS-Focus-Lens-for-CO2-Laser-12-15-18-19-20-25mm-FL-1-4/332449376632?_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20160908105057%26meid%3D70cf8b002f924d4bb3eb36d71d045977%26pid%3D100675%26rk%3D2%26rkt%3D15%26mehot%3Dnone%26sd%3D321078811086%26itm%3D332449376632%26pmt%3D0%26noa%3D1%26pg%3D2380057&_trksid=p2380057.c100675.m4236&_trkparms=pageci%3A13a95051-8d52-11eb-8cc4-129e13dfe8ce%7Cparentrq%3A68db8c8a1780aaf48975e176ffce72b2%7Ciid%3A1The gap between prices from apparently similar lenses in term of features (diamètre, FL, surface state...) is simply to high for being explainable differently (true high quality product vs cheap fake/low grade product), i guess.Cheers.Stéphane

author: angelortega
author_rank: Contributor
timestamp: March 28, 2021, 01:55:11 am
content: hi lambdai just got this these shots using a recycled dual field of view lens assembly from a thorn emi dfov camera. you can see my shots of the lens used posted as recycling a dfov lens for other projects. i have three flir 25mm lenses and one lens has a znse element on backside, two of my cameras are 9hz one is 30hz, the lens with the znse element came from the 30hz camera.maybe the znse lens helps the 30hz camera see better. finding used lenses at real low price is easy the thorn emi camera cost 30k i got mine on ebay for just $255.00 and pulled the lens out. my setup was a tau2 640x480-50mm lens a 75mm extension tube to the lens assembly. so keep trying to reach for the moon with your projects i do and look how far its taken me.