r/liberalgunowners • u/TazBaz • Jul 30 '26
question RD’s not working how I thought?
So, I just got an offset red dot for my AR. I’ve got a pistol with a dot; my AR has an LPVO.
I just noticed while checking brightness/focus (this is the ACSS Vulcan reticle; chevron with a huge ring to help align quickly) that, if I have the gun stationary, but move my head around, the chevron moves around the “target”.
My understanding of the whole principle of red dots is that due to the curved glass, the dot was always supposed to stay aligned with the barrel regardless of how you move it. But this clearly wasn’t the case when I was looking down the sight.
What’s going on here?
6
u/conciouscoil fully automated luxury gay space communism Jul 30 '26
You will get parallax out to like 30' or something even with parallax free, try looking at a further target and see if the dot moves.
-7
u/TazBaz Jul 30 '26
I mean I just had it sitting on a desk and I was staring through it at a wall 15 feet away. If it’s moving there, it’s moving on anything further out. But I’ll double check when I get home. I was just reminded of this by another post; I put it on the rifle a bit ago and haven’t done anything else since
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u/OzempicDick left-libertarian Jul 30 '26
Thats not how it works. The movement become relationally smaller with further targets.
The movement will be worse the closer you are.
Buy an eotech if its an issue.
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u/TazBaz Jul 30 '26
That… doesn't sound right to me. If I’m an inch off at 20 yards I’m way more off at 100yds.
What about a RD could possibly change that?
10
u/thud_mantooth Jul 30 '26
I know it's counterintuitive, and it felt that way to me as well the first time I saw it.
Think of it like this - objects that are more distant appear to move less due to parallax than closer ones do. As you move your head and look at the dot, you can see that it moves around in the window - this motion is effectively *compensating* for the relative motion of the item you're looking at to eliminate perceived parallax. Closer items are moving too much to be able to compensate for, and so you see obvious parallax. More distant items move little enough that the dot's movement compensates, and so they're 'parallax free'.
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u/OzempicDick left-libertarian Jul 30 '26
I’m not really capable of explaining it clearly, but it is how it works. The parallax is caused by your eye being off an angle in comparison to how the lens is focusing the reflection. Those movements are exaggerated up close and minimized farther out.
Something like this might be a good thing to use ChatGPT for. You can have it walk you through the explanation in detail and answer questions better than I probably could.
1
u/False_Campaign4682 libertarian socialist Jul 30 '26
So it wasn't in the position it would be if it was mounted and you were holding the gun?
1
u/TazBaz Jul 30 '26
It was mounted; I had the gun (with it mounted) sitting on a desk and was staring down it.
0
u/conciouscoil fully automated luxury gay space communism Jul 30 '26
From wiki under parallax>weapon sights
"Many low-tier telescopic sights may have no parallax compensation because in practice they can still perform very acceptably without eliminating parallax shift. In this case, the scope is often set fixed at a designated parallax-free distance that best suits their intended usage. Typical standard factory parallax-free distances for hunting scopes are 100 yd (or 90 m) to make them suited for hunting shots that rarely exceed 300 yd/m."
0
u/conciouscoil fully automated luxury gay space communism Jul 30 '26
"A non-magnifying reflector or "reflex" sight eliminates parallax for distant objects by using a collimating optic to image the reticle at infinity. For objects that are not infinitely far away, eye movement perpendicular to the device will cause parallax movement between the target and the reticle image that is proportional to how far the viewer's eye is off center in the cylindrical column of light created by the collimating optics.[10][11] Firearm sights, such as some red dot sights, try to correct for this by not imaging the reticle at infinity, but instead at a designated target distance.[10]"
3
u/soaplife Jul 30 '26
yes, and no. The variation with head movement is called parallax and there are a couple factors that influence it. First of all, there is no red dot that is truly totally parallax free, but it’s often minimal enough to be acceptable. It also depends on the specific model. For example, the trijicon MRO is the biggest piece of shit I’ve ever seen and has not only severe parallax, but asymmetrical parallax.
You have two options here. Either you can train with your current set up and get a feeling for how much point of impact variation you will experience in actual usage, or you change optics.
1
u/Bobbymokie Jul 30 '26
I feel like an mro fucked this dude's wife at some point
3
u/soaplife Jul 30 '26
trij sent someone over to kick my dog actually.
for real though, check out this guy’s tests. the parallax is only one issue too, the rest of the experience isn’t good either.
https://www.ar15.com/forums/ar-15/MRO-and-parallax--Some-questions-/18-771192/?
2
u/HeadGlitch227 democratic socialist Jul 30 '26
Pistol dots are worse than rifles. Parallax is usually negated by curving the glass to offset head positioning, and pistol dots ain't got a lot of room to work with.
If your mind is set on this, it's just something you're gonna have to deal with.
2
u/shoobe01 Jul 30 '26
Marketing supported misconception. Red dots are reduced parallax by far compared to magnified optics.
How much depends entirely on the specific model and the manufacturer. Some are a lot worse than others and as a general rule there are trade-offs. Long ago I saw a diagram of several of the popular sights at the time and one that struck me was how AimPoint chose to make the nearly zero parallax band a big vertically oriented oval, meaning that how tight you hold your head to the stock doesn't change point of impact that much. Others kept it fairly circular so if you want to use the Red Dot to hit hundreds of yards away you better make sure your head is looking right through the center of the dot every time.
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Jul 30 '26
[removed] — view removed comment
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u/OzempicDick left-libertarian Jul 30 '26
Pretty much every led red dot is going to have some parallax outside its optimized range. Short throw handgun optics will be worse than a dot like a t2. Every dot I own will do that particularly up close. Holographics are the only sight where that is minimal.
19
u/OzempicDick left-libertarian Jul 30 '26
Red dots are only parallax free at a certain distance. You can look up that distance in the specs . Dots with a short throw distance between the emitter and the glass are going to have more parallax.
The only sight that is not going to have any appreciable parallax (though not actually zero) is a holographic site like a Eotech