Whilst I have not had a need for a supplemental lens on the CA10 system, I have considered how I might mount a reversed lens assembly on the camera to produce a true thermal microscope capable of 12um per pixel on target
I have yet to carry out any tests however.
With regard to mounting another lens onto the camera head, DYT have made a very nice job of the focus ring that extends out in front of the lens assembly. The deep recess that contains the lens would permit the use of a friction fit ZnSe lens mount in a similar manner to that used on some FLIR E4 close-up lens adapters. It would basically be a ring to old the ZnSe lens and some lightly sprung curved ‘arms’ around the outer edge to press against the walls of the focus ring recess. 3D printed plastic would be an option for this. I would recommend the use of the largest supplemental lens diameter that may be accommodated in the recess along with its mount as this will reduce the risk of vignetting (losing the corners of the image) and most ZnSe CO2 laser lenses perform best towards their central area so try to avoid using the periphery of the lens.
Another mounting option is even simpler ! I bought some push fit lens caps that are made of polythene. They were originally used on binoculars as dust caps. It would be a relatively simple task to cut a hole into the lens cap to accommodate the ZnSe lens. The problem with this approach is the distance of the supplemental lens from the cameras built in lens. The size of the ZnSe lens needs to be adequate to avoid vignetting at this distance from the camera lens. With regard to mounting the ZnSe lens into the lens cap, the plastic resists the adhesive bond of glue but an RTV bead may work
A better approach would be to make a two part lens mount ring that sandwiches the lens cap hole edges between its outer rims whilst also holding the lens element securely. A bit like a plastic rope eyelet in a tarpaulin !
Another option for lens mounting is the use of magnetism but care is needed to avoid the use of uncontained strong magnetic fields that could interfere with the FFC shutter solenoid operation in the front of the camera core. As has been done on mobile phones in the past, a ferrous ring may be attached to the flat focus wheel face of the camera using a double sided adhesive tape. A ZnSe supplemental lens holder is then constructed using a 3D printer or other techniques. Small ceramic magnets may then be attached to the lens holders rear face and these will mate with the ferrous ring on the cameras focus wheel and hold the supplemental lens in place. The design of the lens holder can include enhancements such as centering rings or spigots to keep the lens centred in the cameras focus wheel recesses. It might also be possible to create a ‘Top Hat’ lens mount that positions the lens down in the deep recess of the cameras focus wheel and the magnets remain a good distance away on the rim of the ‘top hat’ at the front face of the focus wheel. A drawing might help here to explain this but alas not possible at the moment. The advantage of the top hat mount would be the closer positioning of the supplemental lens to the cameras lens.
A more drastic option would be to make your own replacement focus wheel with built in threaded mount for supplementary lens mounting. The focus wheel is held onto a flange using the two screws visible in the attached picture. A replacement focus wheel could be printed using a 3D printer but it would be inferior to the excellent metal component used by DYT.
With regard to the error in measurement that the ZnSe supplementary lens can introduce into the system…… yes such an additional optical element will effect the measurement calibration accuracy. How much it effects it very much depends upon the AR coating on the ZnSe lens. ZnSe with no AR coatings has a transmission that is pretty flat over the LWIR band but is only ~70%. A ZnSe lens intended for use with a CO2 laser has a 10.6um AR coating on both surfaces of the lens and the transmission increases to around 99.8% at 10.6um BUT the transmission figure reduces as you move away from 10.6um. A broadband AR coating is really needed to maintain a relatively flat transmission plot over the LWIR band with enhanced transmission. Sadly such BB lenses tend to be expensive and not the cheap lenses available on eBay for CO2 laser cutters etc. Take a look at this document to better understand the transmission of ZnSe.
If highly accurate temperature measurements are required, it may be best to not use a supplemental lens except for visual assessment of components rather than measurement of their temperature.
https://www.lasercomponents.com/fileadmin/user_upload/home/Datasheets/diverse-laser-optics/co2-laseroptics/materials_co2-laser_optics.pdfFraser
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