Protective window for thermal camera - coatings - Page 1
Forum section: electronics / general

author: Mike_91
author_rank: Newbie
timestamp: January 15, 2025, 04:58:39 pm
content: Hi all,I'm looking for a protective window (sacrificial lens) for a thermal monocular (Hikmicro LE10S, spectrum of 8-14 um), the cheaper the better, but it has to have good transmittance.The purposes:1) protect the monocular's lens in airsoft games against a possible hit from the BB (assuming kinetic energy to be <1 J) - even if the sacrificial lens itself gets damaged in such case, it should not shatter into pieces to protect the monocular2) the second use case is protecting the monocular from road debris - I have an idea where I would use the monocular as a "night drive assistance" mounted on a car (a couple of ideas how to mount it on the outside) and transmit the image over wi-fi to my phone (or via CVBS cable which LE10S supports since there is a lag on the wi-fi, to a compatible screen), to help spotting wild animals when driving on wooded roads at night time.I'm aiming at germanium windows, diameter of approx. 20 mm (twice the size of the monocular's lens dia) and thickness of 2 mm - I think this should be sufficient. Coating type is still to be determined, as uncoated Ge lens has transmittance of around 50% in this spectrum, which is too low.But I'm also considering ZnSe windows, which are usually cheaper, however it's a softer material, so I gather not as good as Ge for these purposes.Now, as for the coatings - it can be either AR/AR or AR/DLC.Is the "standard" AR/AR coating good enough in terms of scratch resistance?I know the diamond-like carbon (DLC) layer on top of the AR coating adds extra protection, but at a cost of slightly lower transmittance and higher price.I'm also looking for a supplier where I can buy such thing, and found a few of them (so far best looking one ishttps://www.uqgoptics.com/material-category/germanium/), but some make such windows on custom request and when ordered in larger volume only.

author: Bill W
author_rank: Super Contributor
timestamp: January 16, 2025, 12:17:19 am
content: Standard AR/AR is not going to last long outdoors. It is vulnerable to water which will get in via micro scratches. It is really only suitable as an 'indoors' / internal coating.You can get 'durable' coatings which are close to AR in transmission and stand up to civil use OK - but won't pass military 'sandy windscreen wiper' type tests.The downside is I'm not aware anyone selling windows with AR/DUR singly. The DUR side is a specific coating run that costs 1000's could make in the multiple 100's of windows.A lot of the catalogue sellers like Edmunds are at stupid prices, at least 10x volume pricing.If you are not too fussy cosmetically I could look out and check some of my used windows from Argus cameras - drop me a PM26 or 33mm diaBill

author: Mike_91
author_rank: Newbie
timestamp: January 16, 2025, 08:44:06 am
content: Thank you, BillWhat is the DUR coating? I searched the internet but didn't find any references. Isn't the DLC the type of coating protecting Ge lens from scratches, abrasion and chemicals? I base my knowledge on UQG's spec - they claim their AR/DLC (the side with DLC must be on the outside of assembly, of course) conforms to MIL-C-48497A.

author: Bill W
author_rank: Super Contributor
timestamp: January 17, 2025, 12:36:33 am
content: DLC (Diamond-like-carbon) is a very high spec coating which as you have found is not so great on transmission. However it meets all the MIL-specs for abrasion and water resistance.Classic 'AR' (HEAR, High efficiency anti-reflection) is great on transmission but not so on resistance to wear / water.The 'durables' sit in between. They are an 'on request' coating, only viable if you are buying 1000's and want the extra 15% transmsission. That said DLC is getting better on transmission now anyway.Bill

author: bap2703
author_rank: Regular Contributor
timestamp: January 19, 2025, 07:52:51 pm
content: Would Kitchen plastic film + rubber band be durable enough?

author: Mike_91
author_rank: Newbie
timestamp: January 20, 2025, 08:36:08 pm
content: Quote from: bap2703 on January 19, 2025, 07:52:51 pmNot really, at least not for my applicationIf you're asking not just for fun, then actually LDPE plastic (e.g. many ziplock and kitchen bags are made from it) is somewhat transparent in LWIR spectrum -https://www.researchgate.net/figure/Long-wave-infrared-LWIR-spectral-transmissivity-of-a-low-density-polyethylene-LDPE_fig16_285928780- but its protective ability doesn't need a comment I guess

author: twospoons
author_rank: Frequent Contributor
timestamp: January 21, 2025, 02:02:10 am
content: Ge is more brittle than ZnSe, so might not do so well against an airsoft BB.

author: Bud
author_rank: Super Contributor
timestamp: January 23, 2025, 12:05:17 am
content: If it is possible BB may front hit your camera in the lens while you are looking into it, you have a bigger problem, don't you think.

author: antenna
author_rank: Frequent Contributor
timestamp: January 23, 2025, 06:23:35 am
content: Can you grow nice clean salt crystals big enough? Sodium chloride has good transmittance and is obviously dirt cheap.Sputtertargets.net has flat clear crystals of potassium chloride, and KCl's transmittance band is ideal for IR.

author: bap2703
author_rank: Regular Contributor
timestamp: January 25, 2025, 01:08:23 am
content: Another solution is to use mirrors.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: January 25, 2025, 01:33:05 am
content: I wouldn't give up so easily on plastic films. They do scratch easily and would require some thought/testing to see if they provide adequate protection from the Airsoft pellets. Motorcycle racers use what they call tear offs, which are plastic lens which are peeled of when they get scratched or dirty. If you can replace the covers easily and carry a couple of dozen replacements in your pockets it might work.Since your "particle" of interest has a very specific size have you thought about a wire mesh or screen? An Airsoft pellet would allow a screen with pretty low blocked area, and would probably give minimal diffraction effects.

author: timeandfrequency
author_rank: Frequent Contributor
timestamp: January 25, 2025, 05:48:41 am
content: Hello Mike_91,I would say that 'cheap' isn't the first adjective that comes to mind, when speaking about IR camera stuff.Even if non-cryogenic IR imagers was a big leap forward about 10 - 15 years ago : size, price and complexity was drastically reduced by using innovative microbolometer VOx sensors. At least for the 7 to 14 µm wavelengh span.But let's stay focused on your subject.Those brands manufacture IR windows, check it out :-Wintech-Fluke

author: Mike_91
author_rank: Newbie
timestamp: January 27, 2025, 10:54:57 am
content: Quote from: twospoons on January 21, 2025, 02:02:10 amOK, but on the other hand ZnSe is quite soft, so can be easily scratched, right?Quote from: antenna on January 23, 2025, 06:23:35 amI've come across these, NaCl, KCl, KBr - I guess the transmittance would do the job, but they have one common problem - they're water soluble, even a high humidity can damage them.Quote from: bap2703 on January 25, 2025, 01:08:23 amI've actually thought about it, but that's an extra complexity, and also IR mirrors ain't cheap (Ge window can be cheaper from what I've seen).Quote from: CatalinaWOW on January 25, 2025, 01:33:05 amPlastic films - won't work, not strong enough, airsoft BBs can easily penetrate things like aluminium cans, etc.For regular optics (e.g. collimators) one can use PVC/plexiglass transparent shields with sufficient thickness, but these won't work for thermals ofc.Wire mesh - this is an option, which I'm considering on top of Ge window, for best protection. Many airsoft players use such solution for their optics, as it's relatively cheap and strong. But the BB can shatter into pieces upon impact, and these can still damage the lens, so best to have a protective window behind it.There is a "dedicated" solution out there, for certain thermal optics -https://coldharboursupply.com/products/coti-defender-replacement-germanium-lens- but I didn't get any answer regarding the geometry and type of coatings used from them.As for my use case no. 2, I did a few test drives so far. The camera packed in a ziplock bag (LDPE, I think) as there's lots of dirt on the roads now in winter; the bag noticeably worsens the contrast, but it's still not too bad overall. Video transmitted live via wi-fi onto my second phone mounted just above the steering wheel. The practical benefits of such "night drive assistance" are debatable, but when I was driving through a forest the other day, pitch black, a car coming from the opposite side dazzling me slightly with its lights, I glimpsed at the thermal screen and spotted something "hot" on the right side of the road, so then I looked in that direction, and a split second later when my low beams reached there I noticed a pedestrian walking, wearing dark clothes. I had the "white hot with red highlights" mode on the camera. It's not as handy as having audible warnings when the AI algorithm detects a danger like in some luxury cars, but it can help.

author: artag
author_rank: Super Contributor
timestamp: January 27, 2025, 11:51:33 am
content: Quote from: Mike_91 on January 27, 2025, 10:54:57 amYou have a phone screen that you look at while driving ? Is that even legal ? I don't think it is here (UK). It's certainly not safe - while the thermal vision has some advantages you wouldn't want to drive using only that (there are cold things you can hit as well as warm things) and that's what you're doing if you move your attention or focus there.I don't own a high-end car but I wouldn't expect a separate screen. I'd expect an audible warning or a HUD.Another way of thinking about it is that the ocular is protecting your eye. So what if the lens get damaged ? At least you can still see.Winner, winner, chicken dinner as our host would say.

author: Mike_91
author_rank: Newbie
timestamp: January 27, 2025, 01:38:13 pm
content: I'm not saying I'd be staring at the screen while driving. Just glimpse at it in certain situations, when needed. Just like I can briefly look at a phone with navi turned on, or at speedo to check the speed. However, the number of such useful situations is limited, yet that one example above is apt.I hit a deer on the road once in the past, btw. it was in the UK (and two rabbits and a badger it total, AFAIR; crazy animals that are waiting to jump under your wheels in the last second). Countryside road, speed limit 60 mph, I was driving a bit less that that. Pitch black (trees around), there were cars coming from the opposite side, so couldn't use my high beams. And here comes the deer, most likely it was crossing from right to left. And then it decided to change its mind and turn back. That's when I saw it, turning around slowly on my lane, instead of coming off the road. My choice was to risk a head on collision with another car trying to avoid the deer, or take the hit. But there was no time to think really. Just managed to move slightly to the centre line to minimize the impact area. Of course, I hit the brakes immediately (and the deer, too). Now I'm thinking, what if I had a thermal aid back then, would I be able to spot it earlier...I find the night driving assistance systems quite fascinating... FYI, there are a few different ones out there, e.g. like these which use thermals (passive type):- BMW, displaying on its centre consol screen + warnings:- Audi, using LCD dash to display the image + warning:- Cadillac Deuville, world's first, using HUD display, but no extra warnings, I believe:- or the retrofit options from InfiRay/Thermal Master, with separate screen that you have to mount somewhere in the carQuote from: artag on January 27, 2025, 11:51:33 amNot sure what you meant here?

author: Bill W
author_rank: Super Contributor
timestamp: January 27, 2025, 02:33:32 pm
content: Quote from: artag on January 27, 2025, 11:51:33 amToching a phone (or sat-nav etc) is specifically illegal while driving in the UK, but looking at one is not and would have to come under 'driving without due care and attention'.Strangely looking at and operating a giant touch screen (that at an electronic level is essentially a mobile phone anyway) to adjust the heater is just fine.......

author: SYOM
author_rank: Newbie
timestamp: September 03, 2025, 08:20:50 am
content: Cool project! I’ve done a couple of FPV thermal setups too — keeping the weight down really is the key. I found that adding a bit of foam or rubber to isolate the camera from motor vibrations helps a lot with image stability, otherwise you get rolling shutter effects when the motors spin up. Also, lock the exposure before takeoff if your software supports it, so you don’t get brightness flicker mid-flight.