# glasses and riflescope
**URL:** https://boards.straightdope.com/t/glasses-and-riflescope/199804
**Category:** Factual Questions
**Created:** [September 5, 2003, 7:50pm UTC](https://boards.straightdope.com/t/glasses-and-riflescope/199804 "2003-09-05T19:50:22Z")
**Posts on this page:** 10
**Page:** 1
### Author:  [@viking](https://boards.straightdope.com/u/viking)
#### Post date: [September 5, 2003, 7:50pm UTC](https://boards.straightdope.com/t/glasses-and-riflescope/199804/1 "2003-09-05T19:50:22Z")
I finally got me a hunting rifle and started sighting it in. And I noticed that I had trouble keeping both the target and the cross-hairs in sharp focus, which I had thought was the point of the scope in the first place. Then I read some comment in a hunting mag about (some?) riflescopes being incompatible with (some?) high-index prescription glasses. This makes no sense in the framework of my freshman-physics optics courses, but I’m sure they miss some stuff in that 🙂
So, would anyone have the straight dope on this one? Partly my pragmatic side wants to know if _any_ non-high-index lens (glass? plastic? non-scratch-coated?)will be compatible with _any_ scope, or will I have to take the scope off the rifle and take it to the optician (I somehow doubt strolling into the mall with the rifle would go over too well 🙂 ) Or should I get a better scope that would work with my existing glasses?
But partly my nerdy side wants to understand the physics involved…
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### Author:  [@Padeye](https://boards.straightdope.com/u/Padeye)
#### Post date: [September 5, 2003, 8:05pm UTC](https://boards.straightdope.com/t/glasses-and-riflescope/199804/2 "2003-09-05T20:05:33Z")
Did you focus the scope? You may notice that there is a lock ring where the ocular bell attaches to the body tube. Loosen this ring slightly and you will be able to rotate the ocular until both the crosshair and target image are in focus. DO NOT completely unthread the ocular as you may damage or even ruin the scope. Find an object at a typical huntint distance to train the scop on to set focus.
If your scope has an adjustable objective, and I’m guessing it doesn’t, make sure the objective is set to the same distance at the object.
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### Author:  [@viking](https://boards.straightdope.com/u/viking)
#### Post date: [September 5, 2003, 9:01pm UTC](https://boards.straightdope.com/t/glasses-and-riflescope/199804/3 "2003-09-05T21:01:10Z")
Oh? I got the scope second hand so without any instructions, so that might be it. That would certainly make me feel like a fine fool… I didn’t see any mechanism for focusing it, but I’ll take another look when I get home. It’s a variable power, so the ocular bell, iirc, rotates with respect to the body to zoom. If there’s a lock-ring somewhere that allows focusing, it isn’t where the ocular bell joins the body, but maybe it is somewhere else and doesn’t look obvious enough for idjots like me 🙂
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### Author:  [@Padeye](https://boards.straightdope.com/u/Padeye)
#### Post date: [September 5, 2003, 9:28pm UTC](https://boards.straightdope.com/t/glasses-and-riflescope/199804/4 "2003-09-05T21:28:02Z")
Take another look. I don’t remember ever seeing a scope where the ocular turned with the zoom ring. The lock ring will probably be more obvious now that you’re looking for it so don’t slap your forehead too hard when you find it. Adjust slowly and make sure you’re turning in the right direction.
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### Author:  [@viking](https://boards.straightdope.com/u/viking)
#### Post date: [September 6, 2003, 6:26pm UTC](https://boards.straightdope.com/t/glasses-and-riflescope/199804/5 "2003-09-06T18:26:56Z")
Well, hot dang, there is a second adjustment thing on this 'ere scope. It was just really stiff so I had to yard on it whole-handed rather than the delicate finger-tweaking that had assured me earlier that there was no focus adjustment. It looks like there is no lockring, though, unless the lockring is even more tightly bound to the adjustment ring, and they are now moving together… Thanks, **Padeye**! Of course, living smack dab in the middle of a city, I can’t really focus it on anything hunting distance here, and the range is still closed pending rain, so that’ll just have to wait.
I still don’t quite understand the optics here, though. When I raise it to my eye, looking at my bookshelf a few short yards away, the crosshairs are initially in perfect focus, and the books are almost in focus. Then, try as I might to have anything else happen, the books’ focus sharpens itself, and the crosshairs blur, and I can’t focus back on the crosshairs at all.
But maybe playing with the focus at the range will cause it all to work, despite not understanding how 🙂
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### Author:  [@DougC](https://boards.straightdope.com/u/DougC)
#### Post date: [September 6, 2003, 6:38pm UTC](https://boards.straightdope.com/t/glasses-and-riflescope/199804/6 "2003-09-06T18:38:08Z")
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- Do note: when you focus a scope, first you are supposed to aim the scope at a blank surface or the sky, and turn the eyepiece until the _reticle_ is sharp. Turning the eyepiece focuses the _reticle_, and turning the objective (if it’s adjustable) focuses the _target image_. -And once you focus the reticle, it should stay in focus the rest of the time without adjustment.
~
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### Author:  [@Padeye](https://boards.straightdope.com/u/Padeye)
#### Post date: [September 6, 2003, 10:15pm UTC](https://boards.straightdope.com/t/glasses-and-riflescope/199804/7 "2003-09-06T22:15:06Z")
**DougC** , most hunting scopes don’t have an adjustable objective and in any event its primary purpose is to adjust parallax range not focus. When parallax is adjusted for the wrong range the crosshair and target don’t have the same apparent distance from the shooter’s eye. If the shooter moves his eye off the optical center of the scope the crosshair will move relative to the target and can cause a miss. Adjusting parallax at a specific range will elimate this. it’s most critical for target and varmint shooting where fractions of an MOA count. When I shot ARA .22 benchrest I had to get a scope that would adjust down to 50 yards as the 100 point circle wasn’t much bigger than an aspirin tablet.
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### Author:  [@akirk](https://boards.straightdope.com/u/akirk)
#### Post date: [September 7, 2003, 4:12am UTC](https://boards.straightdope.com/t/glasses-and-riflescope/199804/8 "2003-09-07T04:12:39Z")
Also you might check your “eye dominance” - the eye that contributes most to your vision. Check this link for more info…[http://www.madsci.org/posts/archives/dec98/912662561.Ns.r.html](http://www.madsci.org/posts/archives/dec98/912662561.Ns.r.html)
This was a problem for me because I am right handed, so I assumed that I would sight with the same eye…turns out my left eye is dominant. It isn’t a problem for me when shooting firearms, because I learned so early to compensate, but when I started Archery, I had to switch to left handed equipment because I could not focus.
Hope this helps!
Akirk
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### Author:  [@1kBR\_Kid](https://boards.straightdope.com/u/1kBR_Kid)
#### Post date: [September 7, 2003, 2:08pm UTC](https://boards.straightdope.com/t/glasses-and-riflescope/199804/9 "2003-09-07T14:08:15Z")
Eye dominance is a PITA for me too. I’m also right-handed and left-eye dominant. I also shoot a scoped rifle and wear glasses. FWIW, I’m tired of the hassle of it all and I want to get contacts for shooting only.
Viking-
It could be the scope itself. With the more expensive scopes you aren’t just paying for a name (Zeiss, Nightforce, Swarovski, Leupold).
To get some answers from people with tons of experience go to the forums at [www.benchrest.com](http://www.benchrest.com) and [www.xtremeaccuracy.com](http://www.xtremeaccuracy.com)
It’s a great bunch of people and they will be a lot of help.
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### Author:  [@DougC](https://boards.straightdope.com/u/DougC)
#### Post date: [September 7, 2003, 5:04pm UTC](https://boards.straightdope.com/t/glasses-and-riflescope/199804/10 "2003-09-07T17:04:30Z")
> [@](#):
>
> …When parallax is adjusted for the wrong range the crosshair and target don’t have the same apparent distance from the shooter’s eye… - Pad
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- Yea, , uhhh, , , -I said that… -although people less experienced will see it as a matter of “focus”, because you cannot really “see” parallax error but when a scope is adjusted incorrectly, your eye can only focus clearly on either the target image or the reticle, but not both…
~