What does collimating mean/relevance for thermal clip ons?

[harry_x1]

Hi Folks - apologies in advance for this dumb ass question. I am looking to buy a thermal clip on and have been reading different threads on this topic. I have learnt this much that there is something called collimating the thermal clip on...any idea what this means and whats is the relevance? Apparantely there are thermals which have some kind of prism thing which does not require this collimating manually or something like that...sorry, if my question is not worded accurately, but I guess knowledgeable folks will be able to guess my confusion/question...thanks for your assistance on this

 

[Old Man with Gun]

I has to do with needing to zero the thermal to the scope. I think if the clip on is in perfect alignment it should not be needed. My understanding is some higher end units are built to accommodate some misalignment.

I have a Hogster clip on, I had to sight it in for each rifle I use it on and store the settings for each. I can't just throw it on any rifle and expect to be on target.

 

[Evolution 9]

Two “collimating” methods:

1: “align the screen” clip ons are the cheaper devices to manufacture. You literally sight in the clip on, similarly to sighting in a scope. This must be done for each weapon you intend to use. Additionally, it’s only as repeatable as the return-to-zero capabilities of the mount, as well as the inherent flex of the hand guard, night vision bridge/chassis, etc. Most of us would call a guy an idiot for mounting a scope on a hand guard or chassis rail, but that’s exactly what you’re doing with all of the “align the screen” clip ons. Still, despite these drawbacks, these tend to preform just fine at attractive price points, so they are good options for some users.

2: Prism collimated clip ons are much more expensive to manufacture. The prism overcomes reasonable amounts of misalignment and even hight differences. The technology is over my head, but the end result is the device acts like it’s “passing through” the image with complete perfection such that the scope “sees” exactly what’s actually in front of it just like normal.

This has two primary advantages. 1st, it’s completely repeatable. It doesn’t matter how good the mount returns to zero, or if the mounting surfaces are dusty or muddy, or dented or scraped. Second, you can slap the clip on onto any weapon and shoot with confidence… a buddy’s gun, a new gun, etc. It’s a FAR superior system, and is almost always the choice of serious users like military and LEO because of its bombproof reliability.

These aren’t 100% perfect either, as some of them cause a small shift in POA/POI. This shift is usually VERY small and 100% consistent from gun to gun to gun. So worst case, you know that your particular clip on always moves your impacts down 1/2 MOA regardless of which gun you use. Hardly significant or hard to account for.

 

[wigwamitus]

BTW, it isn't just thermal clipons that can have collimating prisms. Most NV clipons also have collimating prisms. The only NV clipons I can think of that don't are the SIMRADs (PVS-9 and PVS-9a) as they have the mechnical adjustments for collimation instead (late 80s technology). The cheaper and commercial thermal clipons have digital colllimation, ability to move the screen image up down/left right to get them aligned. The higher end military thermal clipons have prism collimation, like the various BAE/Trijicon UTC units or the LWRS-LR.

And in general collimating lenses are not restricted to clipons ... many sorts of binocolulars telescopes etc also have collimating lenses. Read about "optical wedges" or "risley prisms"

If someone decides to go with a commercial unit, be aware the big variables in repeatability for a non-prism collimated unit are YOU and THE MOUNT. The "scope" itself is not a variable (except in rare edge cases, which we could categorize as defects).

1 - Mounts should be solid and adjustable and setup for the rail in question. Not too tight and not too loose. Juuuust right

2 - Mounting process. Practice your mounting process. Put something like a larue rail clipon on your rail to help you index the proper location BY FEEL. So you can dismount and remount in the field without looking. And practice, practice, practice. And per a tip from KSE, lightly grease the mount and rail section occasionally to minimize false friction. This is a KEY trick !

Point is a lot of people ask, "if the xyz scope repeatable" ... and the answer is "NO" ... and an equally valid answer is "YES" ... because the scope itself is not involved in repeatability. The mount is and the primate is. You use a good process and practice, practice, practice and measure your results. After you've collimated, remove the clipon and remount and shoot another group, then dismount the clipon and remount and shoot another group. Then measure the results. That will tell you where you are. And even when you are "experienced" repeat this process occasionally - quarterly ? To verify where you are !!!

==
In my review of the Tig-IR, I was able to remount the thermal clipon and get a one shot kill on a rabbit at 350yds off the tripod. Certainly not HERO stuff, but it shows that it is possible to remount even non-prism collimated thermals and kill smaller targets at some distance. So non-prism collimated thermal clipons are not worthless !!

Night Vision - SOK's TigIR Z6+ Initial Review + Video

Ok, here’s my explanation... That actually makes sense to me. As I have mentioned, Jay has a cool trick for this, but it is his baby, so he should share it.

www.snipershide.com

==
Further note, there's a lot going on - on the rear ends of those UTCs ...

1 - Prism Collimation
2 - Demagnification
3 - Focus

We already discussed collimation a bit so
2 - Demagnification
The front end lenses of the thermal clipons are almost never 1x if the lens is of any size, so that means the backend has to demagnify by the same amount in order for the net magnification thru the clipon to be 1x (else we wouldn't be able to use our reticles)
The UTCs do this demagnification optically (the LWTS-LR does this in software, taking the 2x front lens down to 1x net by a software 0.5x demag).
The optical demagnification results in a cleaner/clearer image but of course, it costs more.

3 - Focus
Hold your hand up in front of your day scope, its really fuzzy. But if you put a jewelers magnifying lens up there it clears up. So the UTCs do this also.

So, it might not be intuitive, but the rear end of those UTCs is where the magic is happening - and that's one reason they cost so much !!!

 

[wigwamitus]

Oh and further clarification.

A key advantage of prism collimated units (both NV and Thermal) is you can move them from rifle to rifle, with no adjustments (prism collimated units unusually - always(?) - don't even HAVE adjustments). Whereas the manually collimated units, moving to a different rifle/scope combination often requires adjustments. So, the SIMRAD moved to a different rifle, have to check it, probably have to adjust it. Tig moved to a different rifle, have to check it probably have to adjust it, though note, the Tig has six saves for collimation !!!