Choosing and adapting a 3rd party lens - helion xq 38f - Page 1
Forum section: electronics / general

author: Fledermaus
author_rank: Newbie
timestamp: May 18, 2021, 05:20:09 pm
content: Hi, I have been looking up thermal camera options for doing bat surveys that don't come with an industrial price tag. The ideal feature set would be to have quality video recording, fov >50, lcd screen (integrated or video out), and modable to an extent (like being able to adapt lenses so I can have a range of fov for different jobs).So, to dip my toe in and start trying things out, I bought a second hand helion xq38f for it's good (and swappable) battery life, apparently decent functionality and reliability, and the removable lens.I have an idea for 3rd party lenses and was wondering if anyone had any advice on how I can proceed with it (or sell the helion and start over): Edmund optics look like they stock off the shelf complete lenses:https://www.edmundoptics.co.uk/f/lightpathr-thermal-imaging-assemblies/39671/I'm looking at the 7.7mm one for it's wide fov and lowish price (provided I can just buy one). I know it is designed for a slightly smaller sensor but I think that will just mean that the edges of the image will be noisy and dark? There's a chart in the spec sheet that suggests so.If this lens could work ok with the helion, how do I get an adapter? The lens has a M19x0.5 thread and the helion's looks like M32x0.7 or something. Will I have to make one? The lens has a working distance of about 10mm so would likely need to go inside the barrel of the helion (the native 38mm is kinda screwed onto the end).TL;DR will the 7.7mm lens from edmund optics (native 320x240 17um) work with the helion (384-288 17um)? Expected image compromise? What would be the best way to adapt it?Many thanks

author: ArsenioDev
author_rank: Frequent Contributor
timestamp: May 18, 2021, 06:06:22 pm
content: So what you're gonna get is vignetting like this crop sensor lens on a full frame, losing outer edge pixels.As for the adapting, I'd do a flanged thread adapter like the attached screenshot, flange to prevent backing down into the assembly, pretty easy to get fabbed by most any machine shop for cheap.

author: Fledermaus
author_rank: Newbie
timestamp: May 18, 2021, 11:01:33 pm
content: ThanksIt would be good to be able to work out what the size of the projected image circle is at infinity focus. I know there are some crop sensor lenses that actually can almost fill a full frame sensor, but maybe with slightly cut off corners and edge distortion, as well as ones like your example where large amount of the sensor isn't used.Thanks for you adapter suggestion, I might see what local shops can do.

author: Vipitis
author_rank: Frequent Contributor
timestamp: May 18, 2021, 11:48:33 pm
content: I am quite surprised to see EO selling at those prices. But it's not Ge or ZnSe. They most likely sell you an adapter as well and feel free to ask them about accurate coverage information - like the image circle.You can find used Ge lenses on eBay and other sources, but you will always have to find a way to adapt them and achieve good focus.Vignetting can be really bad with AGC, so be aware of what options your imager has. And most lenses do need a profile to correct for corner falloff and uniformity anyway.

author: Bill W
author_rank: Super Contributor
timestamp: May 19, 2021, 12:22:24 am
content: Quote from: Vipitis on May 18, 2021, 11:48:33 pmPrices seem about right for moulded chalcogenides, for once EO not making a huge margin. The quoted is the 'optimum' sensor, but Lightpath do acknowledge what works on the datasheets below for other sensor sizes.Full list:https://www.lightpath.com/products/imaging-assemblies/Full datasheets via a distributorhttps://www.amstechnologies-webshop.com/suppliers/lightpath-technologies/?p=1https://www.amstechnologies-webshop.com/media/pdf/55/5f/d2/Thermal-Imaging-Assemblies-Brochure-Lightpath.pdfQuote from: Vipitis on May 18, 2021, 11:48:33 pmThis will be particularly bad for wider angle lenses which was what the OP was looking for. I've seen around 30% drop off even in the expected image area. However as long as there is no huge temperature contrast the effect can be quite minor.Bill

author: ArsenioDev
author_rank: Frequent Contributor
timestamp: May 19, 2021, 05:34:05 am
content: DAAAAAAAAAANG those are some decent priced Chalcogen COTS assys, added to my bookmarks for later IIR experiments.

author: Fledermaus
author_rank: Newbie
timestamp: May 19, 2021, 10:39:40 am
content: That's a good point about the automatic gain. So there is a good chance that the image circle would cover the larger 384 sensor and even a 640 sensor according to the spec sheet, but the image might be unusable without a custom lens profile or manual gain control.The helion xq does allow some control over the image, though it's not even an officially interchangeable lens device, but you can lower the contrast a lot for a very flat look which could make up for heavy vignetting (and does to an extent with the native lens).So what's a good core for building a thermal interchangeable lens camera around?

author: Bill W
author_rank: Super Contributor
timestamp: May 19, 2021, 05:41:12 pm
content: The optical analogy above is OK but may be misleading as in thermal there is no such thing as black. Near the edges the output image is going to be more and more influenced by the temperature of the lens housing.If the lens is calibrated out, the corners are noisierIf the lens is not calibrated out, the corners have less contrast.There may also be a porthole effect, light or dark, depending on the lens housing being hotter or colder than the scene and if the shutter is between sensor and lens.Bill

author: Fledermaus
author_rank: Newbie
timestamp: May 20, 2021, 12:01:48 am
content: Glad you mentioned the "if the shutter is between sensor and lens". My first thought was where else would it be? Then I remembered that the helion has a manual calibration option which I had falsely assumed simply turns off the automatic calibration. It actually does a shutter-free calibration meaning I could still use a different lens and calibrate with an external "shutter". Seems to work ok with the attached lens cap.

author: svgurus
author_rank: Regular Contributor
timestamp: May 20, 2021, 12:22:22 am
content: Good choice, Fledermaus) in my opinion, for field usage with changing lenses Helion is best, therm-app is kinda close) almost bought xq one, but found 2nd xp for similar priceThe thread is m32*0,75, i didnt order adapters but was told it numerous times) my xp is focusing fine with 19mm ther-app lens, guess 6,8 would be fine too if someone sells them now. thermal expert seems to have shorter back length. Putting a lens designed for 320*17 on helion xq is kinda fine too, it has some icons on edges of pictures that i usually crop anyway. You can also try finding thermal-eye 3500as lens, its Ophir 65157 5,8mm f/1 in disguise(if you want to buy that ebay lot of 3 lenses, i'd get one or 2, you will need to allow shipping in Russia) I guess flir tau 7,5-9mm would work too, but they are a bit narrower. btw, i guess all lenses <10-11mm have big distortion, you should consider that too)in the attachment is 3500as lens tried on therm-app without adapter, guess you know that usually ceiling with Armstrong lights looks more straightBut the circle almost fitted 384*17, though ophir claims it was for 320 only

author: svgurus
author_rank: Regular Contributor
timestamp: May 23, 2021, 11:38:13 am
content: Wrote you in PM, Fledermaus) As far as i know, selling outdated non-military non-30hz non-flir tech to Russia is ok, bought 1 lens on ebay already.Anyone used those 3500's? Is front ring used for focusing or you need to rotate whole barrel? Or anyone wants to buy 3rd lens maybe(item #332930840957 on ebay)? Soobrazim na troyih, how we say in my country) Translates somehow like "lets figure out for three of us", usually said while offering to share a bottle