Rifle Scopes Eyeglasses shifting POI with red dot or scope?

[platas]

When shooting an M4 the other day I had a strange experience. Using a Burris TRS-25 Red dot sight on the lowest power setting, I had it well sighted in at 100 yds from a bench with sandbag front rest and rear squeeze bag. Then I moved to some positional shooting: standing using a pole for a rest, shooting off a stool as a front rest, sitting using a sling. In all cases the shots were significantly lower POI than my 100 yard zero from the bench. I'm talking 8-12 inches low. I'm sure it's not shooter error or lack of fundamentals (I usually shoot Expert or Master scores in NRA Matches). My theory is that when shooting from the bench my head is leaning forward and I'm looking through the inside corner or just under the frame of my eyeglasses. Then when doing the positional shooting, my head is more upright so I'm looking more through the optical center of my glasses.
I want to know if anyone has had real world experience with a massive POI shift due to looking through the edge instead of the optical center of their eyeglasses. I suspect this same thing caused me a problem with a 4.5x fixed 100yd parallax scope at 600 yards last year (POI shift several feet right of zero). I'm thinking of ways to test this in a more experimental fashion but I'm looking for "been there done that" experience that I haven't found in any posts so far or google searching. I'm wondering if I need to switch to contact lens and safety glasses and ditch the glasses. I suspect an adjustable parallax scope is less susceptible to the optical distortion at the edge of the lens but can't be sure of that. Thanks in advance for any thoughts on this.

 

[gunsnjeeps]

Do you wear a progressive lens or single vision? I have a friend who swore his sights were bent. Turns out his progressive lens was distorting it.

You have me thinking about why my offhand zero is left of my sitting and prone now. It is new sine we added scopes. I'm going to check it out Saturday.

 

[CoryT]

If the astigmatism is severe, a red dot may present multiple dots, or an elongated dot, or star like pattern, If you use the wrong point, you'll change the POI. If you see a clean round dot, or a clean focused crosshair, you should not have any shift. In the red dot, the target is simply seen through the lens the dot is projected on. Since the image you get in your brain is through a single point in your eyeglasses, it does not matter what point that is (absent focus or the astigmatism problem). In point of fact, with normal binocular vision, you can even close the cap on the red dot sight and shoot just fine, assuming you shoot with both eyes open (as you should). Your brain will combine the two images and you see the dot on the target. this was the princple behind the original red dot sight, the Armson OEG.

In a rifle scope, the image is formed on the crosshair by the objective lens. The ocular just brings that to your eye in focus. Parallax error is where the objective forms the image in front or behind where the crosshair is located, similar to extending you arm and looking at a fingertip , then lining up a finger on your other hand held close to your eye and then moving your head. Either your finger or the point appears to shift location. If you touch your fingers together, your remove the parallax and if you move your head, they stay together.

You can test all of this by fixing the rifle in a rest, then hold your glasses away from your face near where your head would be and look though the lens and move it around. While the entire view may shift, the alignment of the dot/crosshair and target should remain constant.

 

[platas]

Do you wear a progressive lens or single vision? I have a friend who swore his sights were bent. Turns out his progressive lens was distorting it.

You have me thinking about why my offhand zero is left of my sitting and prone now. It is new sine we added scopes. I'm going to check it out Saturday.

I wear single vision lenses and have little to no astigmatism.

 

[CoryT]

Then you have a different problem. I take it it's a standard M4, no free float tube? When zeroing off the bag, how much pressure was applied to the front end? Did the barrel by change end up touching the bag? Those things can move POI a good ways, but still deliver a reasonable group and fool you when you set zero. Just using the sling on an M4 can move the group several inches.

 

[platas]

Then you have a different problem. I take it it's a standard M4, no free float tube? When zeroing off the bag, how much pressure was applied to the front end? Did the barrel by change end up touching the bag? Those things can move POI a good ways, but still deliver a reasonable group and fool you when you set zero. Just using the sling on an M4 can move the group several inches.

standard m4 no float tube. No significant pressure was put on the forend on bench or position shooting. No barrel touching bag or anything else. I'm 99% sure it has something to do with my head position and the change in my eyeglasses related to the red dot. That's why I'm looking for someone with first hand experience with that phenomena. I cannot think of anything else that could move the POI that much (12" at 100 yds)

 

[platas]

You can test all of this by fixing the rifle in a rest, then hold your glasses away from your face near where your head would be and look though the lens and move it around. While the entire view may shift, the alignment of the dot/crosshair and target should remain constant.

This is what I need to test. I assume that the dot/crosshair will move on target due to my lens distortion at the edge of my glasses. If no one replies with first hand experience I'll do a followup test at the range and post results. This one is bothering me.

 

[eastexsteve]

I shoot a red dot on a 9mm AR sighted in at 100 yds. I have single vision glasses. I can shoot with the glasses on or off and the POI doesn't change.

 

[CoryT]

I shoot with progressives and have a pretty bad astigmatism. I see a flared dot in some systems, but no POI shift. If you think about it a little, you'll see it really can't happen. You'd have to see one object, like the target, outside the lens and then the sights in the lens. That would be a problem, but I'm not sure how to arrange that in real life.

This is a lot like the group getting smaller at longer range, lots of people will swear it happens, except, not.

 

[Naaman]

OP, I have done stupider things than what I'm about to suggest, so please don't interpret this as condescension:

If you are certain you've ruled out pressure on the barrel, have you also ruled out the possibility that the zero shifted with recoil? Is the optic and mount properly secured? I had a similar problem to you on a new rifle. The second time I took it shooting, it's zero had shifted. Turned out the mount was not torqued down enough in the first place.

Before doing any elaborate test, I would recreate the scenario wherein the the rifle was zeroed in the first place and see if it's still hitting low.

This is a lot like the group getting smaller at longer range, lots of people will swear it happens, except, not.

I read an article once about a T&E gun which I believe was a GAP rifle (not sure which model... maybe the Rock or Crusader... don't quote me). At 100 yards, they were grouping outside of an inch. At 300 yards, they were under 3 inches (probably were under 2 inches, but my memory of the details is hazy). It happened over multiple loads (if memory serves). Obviously, physics would dictate that this is impossible (or highly improbable), so I'm thinking there may have been something wrong with the sighting system... or possibly the shooter's position relative to the target (I would hope such a shooter would have figured that out before taking the first shot... but like I said above: stupider things have been done by very smart people, and by me as well).

 

[CoryT]

The group thing is mostly shooter induced, either position, lighting, targets, parallax, etc. If you try to duplicate this through two targets simultaneously, you'll see it never happens.

 

[smoothy8500]

I'm looking through the inside corner or just under the frame of my eyeglasses.

Switching from irons to scope in NRA High Power I noticed similar issues with corrective glasses, but not as severe. Either go with plain safety glasses or adjust zero matching with corrective glasses in position.

 

[E. Bryant]

This thread may be of interest:

Observations On The Effect Of Parallax Error When Shooting With An Aimpoint Comp M5 And A Trijicon MRO

Observations On The Effect Of Parallax Error When Shooting With An Aimpoint Comp M5 And A Trijicon MRO Some manufacturers of red-dot sights have made claims that their red-dot sights are “parallax free“. Most of us are already aware that this is simply not true at all distances...

www.snipershide.com

It was certainly educational to me.

With regards to eyeglasses, I have moderate astigmatism, and I have found that looking through the "corner" of the lens (far off the center optical axis) can cause significant image distortion. That being said, I have not noted any change in POI from this effect.

 

[CoryT]

Correct, the image may be distorted, but the effect of POI should be nothing, absent existing parallax issues in the aiming device.

 

[koshkin]

Glasses do not introduce POI soft. However, most red dot sights have some parallax error if the dot is away from the center of the optic. Aside from that, it is usually some sort of a good or shooter issue.

I had the same problem a couple of years ago and it turned out I was a little more aggressive on the trigger than I should have been when shooting offhand. The weird thing was that I was very consistent with it, so group size was the same, but the whole group was a few inches lower offhand compared to standing. I think I was trying to tie the sit, so when I focused on not doing that, the shift went away.

ILya

 

[platas]

have you also ruled out the possibility that the zero shifted with recoil?

I had thought of that as a possibility. The m4 has a heavy profile CAR barrel so it's muzzle heavy. It's possible some poor recoil management was in play. I need to sort that out too. I believe the optic is very securely mounted.

 

[smoothy8500]

Glasses do not introduce POI shift.

So it is probably more of a shooter induced parallax issue since the eye position is not the same when standing, seated, or prone?

 

[koshkin]

So it is probably more of a shooter induced parallax issue since the eye position is not the same when standing, seated, or prone?

That is a possibility. I've seen a ton of sample variance with TRS-25.

ILya

 

[gunsnjeeps]

At 100 yards I notice about an inch and half to two inch shift to the right from a good centered off hand group to both sitting and prone. Didn't have it with irons, could be head position because I'm not shooting enough. Thought it might be new glasses last summer. Coincided with more travel.

I have a 200 yard match Saturday. I'll take my time and see what happens.

 

[wade2big]

My stepmother shoots roughly 6 inches low and four inches to the right. She is relatively consistent there. Now she isn’t a marksman and only shoots a few rounds before a hunt and only takes shots around 100 yards or left on game. Her rifle has to be sited in for her only. First time I ever seen this happen. She wears glasses with bifocals and figure that has to be it.

 

[Ravenworks]

This is what I need to test. I assume that the dot/crosshair will move on target due to my lens distortion at the edge of my glasses. If no one replies with first hand experience I'll do a followup test at the range and post results. This one is bothering me.

I've run just about any type of crane setting steel or pouring concreate and an excavator

I had bought new glasses and the next day I couldn't judge distant or depth.
My point-
I had my glasses on and very seldom work off a computer for distant.
I hit a cement truck while I was 300 feet up and 80 feet from center.
By hitting it I mean a tap.
I've always been steady as a judge but doing what I do there is no error for mistakes.
Do I think prescription glasses will effect your vision through distortion , absolutely.

 

[Naaman]

I've run just about any type of crane setting steel or pouring concreate and an excavator

I had bought new glasses and the next day I couldn't judge distant or depth.
My point-
I had my glasses on and very seldom work off a computer for distant.
I hit a cement truck while I was 300 feet up and 80 feet from center.
By hitting it I mean a tap.
I've always been steady as a judge but doing what I do there is no error for mistakes.
Do I think prescription glasses will effect your vision through distortion , absolutely.

I can second this. I have had trouble playing basketball when wearing a new prescription. I would throw straight, but air ball short of the hoop.

 

[aljones_315]

just my 2 cents i had 20/580 right eye and 20/640 left eye pretty severe astigmatism . the best money i ever spent in my life was getting lasix its been nearly 4 years and holy shit what a quality of life difference it has made. everything from shooting to water skiing feels like a new found freedom if its even a thought in your mind get it done. it cost me $6422.50 with no insurance coverage at all and id do it again in a heart beat my shooting game has improved 10 fold and i enjoy it much more when im not fighting prescription glasses

 

[platas]

just my 2 cents i had 20/580 right eye and 20/640 left eye pretty severe astigmatism . the best money i ever spent in my life was getting lasix its been nearly 4 years and holy shit what a quality of life difference it has made. everything from shooting to water skiing feels like a new found freedom if its even a thought in your mind get it done. it cost me $6422.50 with no insurance coverage at all and id do it again in a heart beat my shooting game has improved 10 fold and i enjoy it much more when im not fighting prescription glasses

I can't afford Lasik right now but I'm curious to try contact lenses and see if that helps.

 

[aljones_315]

I can't afford Lasik right now but I'm curious to try contact lenses and see if that helps.

i wore contact lenses foe 23 years it was very nice while it lasted working outside in constantly blowing wind and endless dust finally made my eyes reject the soft contact lenses where i couldnt bear to keep them in more than a few hours before my eyes wouyld puss up and swell shut good luck with whatever you decide to do

 

[wade2big]

i wore contact lenses foe 23 years it was very nice while it lasted working outside in constantly blowing wind and endless dust finally made my eyes reject the soft contact lenses where i couldnt bear to keep them in more than a few hours before my eyes wouyld puss up and swell shut good luck with whatever you decide to do

I wore contacts for 9 years until my eyes just couldn’t take them anymore as you. I had lasik at 19 years old. My eyes hadn’t changed in several years is why I was a candidate so young. That was 18 years ago and still going strong. Best decision I could have made.

 

[platas]

I did more testing of the red dot optic at the range Monday. I wasn't able to observe much movement of the dot with the rifle firmly in a rest when looking through the edge of my eyeglasses. When I had the dot further away from center (moving head and cheek weld around) it did seem to affect the red dot location on target slightly. I tried to consciously keep my head and eye alignment such that the red dot was just above my front sight post. My results and hits on 8" steel at 100yds were much more consistent. I was also able to call my misses when I had poor trigger break. I think I just need to practice more with this platform as the recoil management is a lot different than my competition service rifle that weighs almost twice as much.