Why are thermal scopes mounted so high and to the rear...??

M

Micanopy Mike

New member
All the photos I have seen of both the FLIR RS thermal scopes and the new IR Hunter thermal scope shows them mounted quite high above the top of the barrel. This makes it very difficult to get a good stable cheek-weld on the butt-stock. Is this done intentionally or is there some design constraint that requires this extra high mounting? Back-up/flip-up iron sights is one one reason for mounting optics such as red-dot scopes an extra inch or so higher so that they co-witness in case of optical or battery failure. This makes sense if you are somewhere over in the sand-box fighting hadjis where battery failure or optical damage could easily result in your demise. However, in the arena of sport hunting, the need for co-witnessing with iron sights is not so critically important. It might be just me, but rifle and carbine classes at Gunsite and Thunder Ranch have all emphasized setting up rifle optics as low as possible so as to provide a proper cheek-weld. Every extra 1/2-inch of mounting height makes it just that more difficult to "snuggle-down" into a stable and repeatable hold.

Along with this same topic is the issue of seeing so many rifle optics mounted quite far to the rear. Unless you have a very short neck, this forces most shooters to scrunch their head to the rear in order to provide for proper eye-relief as well as avoiding cut eyebrows from recoil. As with optics that are mounted too high, this also makes acquiring a stable and repeatable hold more difficult.

Somebody has gotta 'splain why so many scopes are mounted so high and so far to the rear....
 
Mike....

Just mount the unit on an AR and you can adjust your cheek weld and the stock length to suit your physical stature. You should be able to "snuggle-down" nicely with this Magpul PRS stock.



qB1jii8.jpg
 
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IMO NV scopes & thermals could be a lot lower to the bore w/out having to add a cheek pad or spend $250 on a stock to make it work.
 
Originally Posted By: 5spdIMO NV scopes & thermals could be a lot lower to the bore w/out having to add a cheek pad or spend $250 on a stock to make it work.



+1 what he said!

Although I do find it easier to get a good feel with my D740 night set up because I am usually sitting on a stool, using shooting sticks versus the prone position which is mostly done during the day.
 
Originally Posted By: Micanopy MikeAll the photos I have seen of both the FLIR RS thermal scopes and the new IR Hunter thermal scope shows them mounted quite high above the top of the barrel. This makes it very difficult to get a good stable cheek-weld on the butt-stock. Is this done intentionally or is there some design constraint that requires this extra high mounting? Back-up/flip-up iron sights is one one reason for mounting optics such as red-dot scopes an extra inch or so higher so that they co-witness in case of optical or battery failure. This makes sense if you are somewhere over in the sand-box fighting hadjis where battery failure or optical damage could easily result in your demise. However, in the arena of sport hunting, the need for co-witnessing with iron sights is not so critically important. It might be just me, but rifle and carbine classes at Gunsite and Thunder Ranch have all emphasized setting up rifle optics as low as possible so as to provide a proper cheek-weld. Every extra 1/2-inch of mounting height makes it just that more difficult to "snuggle-down" into a stable and repeatable hold.

Along with this same topic is the issue of seeing so many rifle optics mounted quite far to the rear. Unless you have a very short neck, this forces most shooters to scrunch their head to the rear in order to provide for proper eye-relief as well as avoiding cut eyebrows from recoil. As with optics that are mounted too high, this also makes acquiring a stable and repeatable hold more difficult.

Somebody has gotta 'splain why so many scopes are mounted so high and so far to the rear....

The housing on a thermal scope is designed differently than a typical day scope. For instance, both the ATN ThOR and FLIR RS units use the same body size, mount, and eyepiece on units with different lens sizes. The ThOR has the same body for 19mm,30mm,and 50mm with a riser on the mount for 100mm units. The FLIR RS units have the same body for the 13mm, 19mm, 35mm, and 60mm.

Look at the gap between the bottom of the objective lens and the rail on the 30mm ThoR vs a 50mm ThOR and the 19mm vs a 60mm RS.
ATN-ThOR-336-3x-336x256-30hz-7T.jpg

ATN-ThOR-320-3x-320x240-30hz-4T.jpg

FLIR-RS32-2.25X-2T.jpg

FLIR-RS32-4X-2T.jpg


As for "so far to the rear" the eye relief is also a little different on thermal/digital systems vs day optics. I actually like it better because the relief runs right up to the eye piece so most thermal scopes work well as thermal monoculars. Ever try that with a day scope? Not sure why anyone would, but it doesn't work at all.
 
Originally Posted By: 5spdIMO NV scopes & thermals could be a lot lower to the bore w/out having to add a cheek pad or spend $250 on a stock to make it work.

Most people that can afford a $5k to $10k thermal scope would be able to buy a $250 stock if needed.
 
The reason for why these and other dedicated NV riflescopes are mounted high off the barrel is a product of design constraints. The same design constriction is in place on standard daytime optics with larger objective lenses (50 or 56mm) which require high scope mounts to clear the barrel. Consider that most high end dedicatd NV scopes with fixed 4 or 6x powers have front objective lenses of 60mm to over 100mm in order to allow them to function well in low light conditions. These scopes tend to come with built in mounts since they have to be mounted significantly higher than daytime optics. The only problem this creates is cheek weld and making sure you properly sight in your weapon at the right distance since the sight plane will be significantly higher than the bullet plane when it leaves the barrel. For close range shooting you need to remember that at shorter distances (25 to 50 yards) the bullet will be hitting significantly below your sight plane. If you sight the weapon in so the sight plane crosses the bullet plane at a close range (50 yards) this can cause longer shots to be too high especially for flat shooting calibers. As long as you remember this concept and make adjustments to the stock to offset cheek weld you should be ok with these types of weapon sights. Kevin
 
Any long range NV or Thermal scope is going to have an objective diameter of 100mm or greater, some are 240mm, this is to accept as much light as possible, and means a high mount.
 
Originally Posted By: Gman757Originally Posted By: 5spdIMO NV scopes & thermals could be a lot lower to the bore w/out having to add a cheek pad or spend $250 on a stock to make it work.

Most people that can afford a $5k to $10k thermal scope would be able to buy a $250 stock if needed.





Maybe all of us that don't have an extra $250.00 laying around could send you our addresses and then you could send each of us one and maybe a new scope while you are at it??

Thanks in advance Mr. Money!!!
 
Hmmmmm.... Thanks for the responses, but I suppose I was not clear in wording my question. There is at least one "hunter-grade" thermal rifle scope that has a 640 X 480 (17 uM) core resolution with a 35mm focal length objective lens (same as the FLIR RS64 and IR Hunter) and an 852 X 600 pixel OLED display. It is somewhat smaller than either the RS64 or the IR Hunter but it is about a whole pound lighter. The center-line of its optics axis mounts almost a full inch lower than either the FLIR RS64 or the IR Hunter. A very compact unit, but it does not have as many neato-keeno features as the IR Hunter. Info sheet and photos of the unit are here:

http://www.pyser-sgi.com/images/added/pdf/PNP-MTHDS%20and%20MTHDES.pdf

As for my question asking why so many rifles are seen with their scopes (standard or thermal) mounted very far to the rear, I have seen a lot of relatively small size scopes set waaaay back which makes no sense to me. At our local range I often see shooters that need to crank their heads back to use their scope. I would post a photo example here, but when I click on the forum icon to "enter an image" with a post I get a message saying to "...enter the URL for the image you wish to post..." If I have a small file size .jpg photo in a folder, how do I include it with my posting message?

Thanks--

Mike/Micanopy, Flori-DUH
 
Mic Mike,
I positioned my rs32 just far enough forward to allow easy charging handle manipulation. Keeping it as far back as I can makes it easier for me to use with an eyeshield during dawn-day-dusk periods. I find that any stray light makes it hard to use/sight.
If I want a little more room at night when light is not an issue, or for a different shooter, I adjust my stock. Recoil for me is not an issue as I use it on 223 ,300blk, and 7.62x39 ars. I also replaced the factory rubber eye cup with a neoprene one that allows comfortable full contact .
I don't believe the housing on mine would allow much lower seating.
I position my day optics as far forward as I can. Other than the eotech, most of my scopes are long enough that even with cantilever mounts they barely clear the charging handle. I think the rs32 is short enough that it just looks further back when positioned at an equivalent ocular distance.
 
Interesting unit you posted, also. Gonna look into it.
I notice their ad pics show the eyecup obstructing the ch, LOL... Maybe that's just how the cool kids do it?

Honestly, for an optic that I need close eye contact with I'm not sure a lower/forward position would work well for me on an ar.
It would be more ideal on a bolt gun for sure.
 


he has no problem with sight over bore height, and its never been a problem for most of use who know how to compensate under 50 yards. how many years has this not been a problem to guys to who shot a scoped M1A, Enfield's, and even gen 0 on M2's ect, ect, oh lets not forget the old gen2 on the carry handle of the M-16

point being you are not going to get the line of sight- line of bore system such as a aim point/Eotech with the amount of glass needed to preform beyond 100 yards!
 
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one other noted point being that the farther forward the lens is the more reward light is exposed, exposing yourself? yes it would be great to have a scout rifle forward mount ,low profile, in line with bore, with no back wash, requiring no hold off below 50 yards , and good to 300 yards.

????
 
I guess a simple answer to your question is...they just are. There are reasons why, and I think some have tried to explain them but there is no getting around the height issue at this point.



Originally Posted By: Micanopy Mike If I have a small file size .jpg photo in a folder, how do I include it with my posting message?




You will need to host your image somewhere to post it. You can use photobucket.com, box.com, or the PM photo housing gallery here http://www.predatormastersforums.com/forums/ubbthreads.php?ubb=postlist&Board=80&page=1
In the image housing gallery chose the image manager button when making a post. Select the file on your computer and upload. Hope that helps.
 
Originally Posted By: Micanopy MikeAll the photos I have seen of both the FLIR RS thermal scopes and the new IR Hunter thermal scope shows them mounted quite high above the top of the barrel. This makes it very difficult to get a good stable cheek-weld on the butt-stock. Is this done intentionally or is there some design constraint that requires this extra high mounting? Back-up/flip-up iron sights is one one reason for mounting optics such as red-dot scopes an extra inch or so higher so that they co-witness in case of optical or battery failure. This makes sense if you are somewhere over in the sand-box fighting hadjis where battery failure or optical damage could easily result in your demise. However, in the arena of sport hunting, the need for co-witnessing with iron sights is not so critically important. It might be just me, but rifle and carbine classes at Gunsite and Thunder Ranch have all emphasized setting up rifle optics as low as possible so as to provide a proper cheek-weld. Every extra 1/2-inch of mounting height makes it just that more difficult to "snuggle-down" into a stable and repeatable hold.

Along with this same topic is the issue of seeing so many rifle optics mounted quite far to the rear. Unless you have a very short neck, this forces most shooters to scrunch their head to the rear in order to provide for proper eye-relief as well as avoiding cut eyebrows from recoil. As with optics that are mounted too high, this also makes acquiring a stable and repeatable hold more difficult.

Somebody has gotta 'splain why so many scopes are mounted so high and so far to the rear....

Not sure what you mean about the RS line having a high cheek weld? There are a basically the same height as an ACOG, Elcan Specter DR and my cheek weld does not change from one optic to these others. The IR Hunter is just a 1/8" higher but still no ill effects of proper cheek welds.

Not if you were talking about the BAE PAS-13, these are indeed high as these were designed at the onset for crew served weapon platforms where there is not an intended cheek weld for these platforms.

Dedicated NV scopes on the other hand with large objectives are a bit higher due to the room needed for these optics.
 


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