I haven't tried it yet ... and would not try it except you aren't the first person to ask. So maybe I will try my mk3 60mm as a clipon (briefly) one afternoon and write it up ... but I'm so busy using it as a dedicated thermal scope, I have a hard time finding time to try it as a clipon !
In general, thermals either have a diopter lens on the back or a collimating lens on the back. The diopter lens is designed to "focus the reticle" for humans with imperfect eyeside (such as moi). The collimating lens is designed to align the effective optical center of the clipon to the day scope optical center. Diopter lenses cannot do that.
So, when I have used diopter thermals as clipons, I leave the thermal reticle and the day scope reticle both turned on and visible. When I zero the "clipon" to the day scope, I co-witness the reticles at a particular distance, like 50yds or 100yds. When I remount the clipon later, I can observe if the reticles are still aligned. If not, I can rezero the clipon.
Summary, diopter lens thermals are not designed to be clipons. They can be used as such in a pinch, but the accuracy will not be high. When remounting, expect to live with some POI to POA mis-match or expect to re-zero. Do not expect the accuracy to be much beyond the distance you zeroed the (nada) clipon.
And also, when I've done it, both devices were 1x.
Another aspect is parallax. After clippin on .. with both reticles visible. Move your head. If there is a lot of movement of the clipon reticle, then you have parallax. Try adjusting the day scope parallax adjustment to minimize that parallax. Don't think about "focusing" on something you can see, just look at the reticles and minimize the movement of the clipon reticle with respect to the day reticle, while you move your head back and forth.
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But mainly, my advice, is, if you want a real thermal clipon to work with a real day scope like a Kahles, then I would go ahead and get a real thermal clipon. There are three, that pop into my head that support 10x or more magnification on the day scope:
N-Vision TC-50 - $11,000
https://www.adorama.com/nvtc50.html?gclid=EAIaIQobChMItJXS7Jjp2AIVSZd-Ch1IsQqREAQYAiABEgKI2PD_BwE
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FLIR T-75 - $11,900
https://pr-infrared.com/product/flir-thermosight-t75-advanced-thermal-sight/
And BTW, I've seen a 10% off coupon on the PR-Infrared site. Call them and say "I will buy today if I can get 10% off - and maybe you can. Then price would be $10,700 (but mean it if you say it
)
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BAE UTC-x - $25,000
https://www.greyfoxindustries.com/products/utc-x
You might be able to find a used one for less. You might be able to find a new one for less. The search for a "legit" UTC-x that BAE will service if it breaks is a long process. I speak from experience
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Any who, yes all those options are over $10k ... but if you want 10x+ magnification support on the day scope with repeatability in mounting, then you need to get a real thermal clipon.
And the MK3 60mm are not free, new ones often sell for $8k plus.
The Mk3 60mm is a thermal rifle scope and due to its 4.5x optical magnification it is a decent long distance spotter as well. It is not purpose designed as a thermal clipon since it does not have a collimating lens on the back.
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Another option is the SNIPE-IR, you can squeeze 7x (I was ok with 8x) out of it ... but the collimating lens on the one I had was not near the ball park of the "real" thermal clipons I listed above. I had to make significant adjustments when mounting it to a new rifle.
WIth the UTC-x, no adjustments are needed or even possible. Just mount and shoot and it is dead on to the POI of the day scope.
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Now all that said, what are you trying to do with that Kahles and a thermal clipon? Hunting out to 300-400yds at 6x? In that case, there are various other options that will work at 6x. Like the L-3 LWTS. Most of these options are designed to be 4x support for the day scope, but you can squeeze 6x out of them with a little fuzz. Even the Pulsar 50mm "front attach" thermal clipon will get you about 5x magnification on the day scope for well under $5k and you can squeeze that to 6x with a bit of fuzz.
Where the 10x+ clipons work is for target shooting out behind 500yds ... out to say 900yds on heated steel. That's what I do with my UTC-x.
We use 12x24 inch silhouettes and beyond 900yds with any wind, those are tough to hit. But we practice out to 900yds and they work out that far.
That said, if you want to target shoot steel at night out to 900yds, then a PVS-30 refurb and a good illluminator will get that job done for under $6k for sure (you might have to change your rings).
