Mystery Supplemental Telephoto lens - Big and beautiful X2 ? - Page 1
Forum section: electronics / general

author: Fraser
author_rank: Super Contributor
timestamp: February 19, 2025, 02:54:55 pm
content: It is Mystery lens time at the EEVBlog thermal imaging forumI stumbled upon a large supplemental lens on ebay that caught my attention as it has a bayonet mount similar to that of the AGEMA/FLIR PM series industrial cameras that I collect. It definitely was not a FLIR lens though as it is totally anonymous except for some labels placed on the barrel.The lens appeared to have some nasty damage to the front lens element so I negotiated on the asking price with the seller. Upon receiving the lens I found that it did, indeed, have some scratches on the front lens element but cleaning revealed that what appeared to be more serious damage was just contamination by something sticky smeared on the surface. The lens is actually in very serviceable condition with no significant damage to the lenses or barrel. I had myself a decent supplemental telephoto lens ripe for adaption to other thermal cameras.Brief testing shows it to be something like a X2 lens operating in the LWIR band, so a useful lens to have around. This is not the sort of lens you mount in front of an Infiray P2 though It is a large aperture lens designed to mount in front of a thermal camera that possesses a large objective lens.... just like the FLIR PM series cameras. The front lens element is 90mm in diameter and the rear lens element is 50mm diameter. The large diameter rear lens is designed to match a similar size objective lens on the thermal camera. For me, this sets the likely date of manufacture as the 2000's, when large diameter LWIR objective lenses were common due to microbolometer pixel sizes in use at the time.For those unaware, it is quite common in thermal imaging systems to have optional supplemental lenses that mount onto the front of a cameras fixed lens. Thermal cameras sometimes employ internal lens systems that would make changing lenses technically challenging, so adding a supplemental Wide angle, Telephoto or Macro lens was considered a sensible solution. The wide angle lenses were often X0.5 and the Telephoto X2. On an industrial camera equipped with a 320 x 240 pixel microbolometer and the common 24 Degrees HFOV lens this provided the user with the option of 48 Degrees HFOV and 12 Degrees HFOV. These fields of view covered the majority of Industrial needs and additional lenses were sometimes available with more specialist fields of view where needed. The cameras used supplemental lens measurement correction factors to maintain temperature measurement accuracy. Various methods were used to allow the supplemental lens to identify itself to the host camera but some cameras needed the user to either enter the correct lens type in use or the stated transmission figure for such in the user configuration menu.So back to our mystery lens.....The lens is equipped with a bayonet mount for attachment to the host camera. It was common to find bayonet mounts and screw thread mounts on supplemental lenses. Inframetrics uses both during their various camera generations. The bayonet mount on the AGEMA/FLIR PM series cameras uses three pins on the host side that engage with the bayonet slots in the supplemental lens barrel. The mystery lens has a barrel diameter slightly larger than that used with the FLIR PM series though so it is not a 3rd party lens for a FLIR camera. The camera that the mystery lens fits with have a supplemental lens mount in front of its objective that can accept a lens barrel of 65mm and likely engagement depth of around 10mm. Three spring loaded ball bearings are used to maintain a preload in the bayonet mount so there will be a flat face in the host cameras lens mount against which the ball bearings will press. There could even be dimples into which the ball bearings engage to secure the lens from easy rotation.As has already been stated, the camera to which this nice supplemental lens belongs will have a large objective lens of approximately 50mm diameter. That immediately excludes most common 'modern' cameras as they tend to use far smaller diameter lenses. That said, this lens will happily work into a modern thermal camera provided the HFOV is reasonable for a beam path match. I can just see the diminutive Infiray P2 strapped to the rear of this 'monster' lensWell if it works, why notWell dear readers, if you have stuck with me this far..... the challenge...... does anyone recognise this lens or the description of the lens mount that I have detailed ? I have looked at common industrial cameras from the 2000's era and come up empty so far. I even wondered if I had it wrong and this is a X2 lens for a modern thermal imaging rifle scope or surveillance scope that has a 50mm objective. The old FLIR HS series allowed the use of supplemental lenses but they were very different to this monster lens. I have yet to find a thermal scope that has a suitable bayonet mount for a supplemental lens. Then there is the labelling on the lens. It clearly states camera 1 in the German language (its sellers origin). The German origin of the lens even had me looking at InfraTec and Jenoptik cameras, but no match to date.It is not essential to know the origins of a lens like this in order to use it with other makes of thermal imaging camera. Supplemental lenses are very different to primary lenses in this respect as there is not the issue of correct back focus distance and, within reason, image circle size. All it takes is a 3D printed mounting adapter to match the needs of the supplemental lens mount and that of the host camera.Fraser

author: Fraser
author_rank: Super Contributor
timestamp: February 19, 2025, 03:15:00 pm
content: The supplemental lens mount of a FLIR PM series camera. The original host lens mount for the mystery lens will have looked similar to this and employ pins into which the supplemental lens mount engaged. Sadly the mystery lens is not a direct fit on the FLIR PM series cameras, but I could use it with such if I created a mounting adapter.Fraser