Many talented shooters will never nail a sub-MOA group due not to their skill, but to misunderstanding a scope‘s parallax adjustment and what it’s for. Hint: it ain’t “side focus.” Not really.

For scopes with adjustable parallax — which is going to be the majority of them with magnification over, oh, 8x or so — the first thing to know is to ignore the yardage markings on the parallax adjustment dial. On the vast majority of optics, even the high-end models, it simply isn’t accurate. Instead, you’ll want to determine the correct adjustments yourself via the method we’ll get to below.

Shout out: the parallax adjust on my SIG TANGO6 5-30x is one of the few that I’ve found to be dead-nuts on. As its little brother, the previously-reviewed TANGO6 3-18x (which I traded towards the 5-30x) was also perfect, I don’t think I simply got a ringer.

First, a step back . . .

What does parallax adjustment actually achieve? What is it for?

The — and I mean THE — purpose of a riflescope‘s parallax adjustment is to put the reticle on the same focal plane as the target. The result of doing this correctly is that, should your eye move around in relation to the scope, the reticle doesn’t move around on the target.

While I understood the result and why it’s important, I didn’t truly understand the “same focal plane” thing (I didn’t even bother to understand the “how it works,” honestly) until Ladd Hall provided a blatantly clear visual demonstration for me at Mill Creek Shooting Resort:

Look across the room you’re in and pick a small target. Yes, right now. Could be 10 feet away could be 50; doesn’t matter. Now stick your thumb up like you’re hitchhiking, close your non-dominant eye, and put that thumb right on target. Keeping your thumb dead still, move your head around a little. Your “reticle” (thumb) walks all freakin’ over the target.

Now, either get a helper or just imagine that somebody goes and physically places their thumb on your target. Move your head around as much as you’d like, and your “reticle” stays dead-on still, right on the bullseye.

The difference is focal plane. In the first scenario, your thumb is on a focal plane a few feet in front of your eye, while the target is on another plane farther afield. In the second scenario, the thumb is on the same focal plane as the target. Changing the angle between your eye and the target doesn’t move the reticle on the target, because they’re in the same place and the angle to both of them is always the same.

If you have an absolutely perfect cheek weld and place your eye in exactly the same location behind the scope on every single shot from every single firing position, you don’t need to worry about getting your parallax adjustment correct. Then again, you don’t actually exist. For the rest of us…all of us:

Adjusting For Parallax

Look through the scope and place the crosshair on a nice, small bullseye. With the rifle remaining as still as physically possible — ideally it’s on a rest or bipod setup of some sort — move your eye around without leaving the exit pupil (the image doesn’t disappear). Does the crosshair stay on the bull, or does it wander around? If it wanders, you need to adjust the parallax dial until it doesn’t.

This might be on the matching yardage mark on your scope’s parallax adjustment, but it probably won’t be. This might put the image in perfect focus, but it very well may not. Maybe the most common mistake shooters make is simply dialing to the mark on the parallax dial. Second most common: using it as a “side focus” and dialing until the image is as clear as possible.

The bottom line is that it doesn’t matter if the image is perfectly clear. It just has to be clear enough to identify the center of your bullseye. Zero parallax error comes first. If zero parallax and a clear-enough image don’t overlap, you have a faulty scope. Additionally, it absolutely doesn’t matter if your target is at 100 yards and you ended up parallax-free on your scope’s dial at the 70-yard or 135-yard mark. As long as there’s a way to dial out parallax at the distances you shoot at, you’re good.

Indeed, parallax needs to be adjusted every time the distance to your target changes. Leaving it adjusted for 100 yards and then engaging at 500 yards may result in a couple minutes of parallax error in the reticle. Forgetting to turn that parallax dial is a big mistake.

In The Field

While adjusting your scope’s parallax setting for every distance sounds slow and cumbersome, it’s something you should only have to do once at various distances. Basically, keep notes on paper or in your head. Once you know that a specific scope’s parallax adjustment dial should be at the 75-yard mark for a 100-yard target, 200-yard mark for a 200-yard target, 460-yard mark for a 400-yard target, infinity mark for anything beyond 500 yards, etc. etc., you shouldn’t have to do the head-wiggling test again.

But if you want to get the most accuracy out of your rifle, don’t avoid the head wiggle. Don’t avoid the effort needed to tinker with that dial until your parallax error is truly gone.

Dialing in “side focus” could leave you with a reticle that walks an inch off the bull due to moving your eye just a few millimeters in any direction behind the scope. Shot-to-shot, you could be doing everything absolutely perfectly behind a quarter-MOA-capable gun and never beat a one-minute group.

Parallax Error

Now that we know what parallax error is and what causes it, we know how important it is to adjust for it. Take the time, look a little silly wiggling your head around behind the scope, and correctly dial out your parallax error. Your groups will thank you for it.

38 Responses to Scopes For Beginners: Parallax Adjustment

  1. Besides sound fundamentals, solid equipment, and match ammo, parallax (which my stupid Samsung S8 wants to spell with just one l), is crucial in getting from 1 1/2 MOA to sub MOA.

    • I know this is way off topic, but just how hard is it to fit a barrel to a 1911, an old one, not them series 80 s ? I been wanting to do it myself.. is it as hard as some make it out to be? I just want a 7 yard shooter, nothing match accurate

      • You got it. We’ll be hitting more “guns for beginners” category stuff, including a couple more scope-related ones (was planning on writing about diopter adjustment next). There’s likely a bit of an info gap directed towards new shooters that truly starts at the very beginning, like “what is a ‘muzzle'” and other terminology stuff to “how to load a magazine” to whatever else. We’re going to start covering the bases.

        • And, I know I speak for everyone here when I say. . .

          Ok, so what knob is for “side-focus” then? Cause, I’m outta knobs.

          : )

          /sarc (as far as you know)

  2. I use the parallax adjustment on the range. In the field I set it for 200m in open country and for 100m in close country.

    Keep it simple.

    • Most scopes with fixed parallax will have the distance set according to applcation. Typically 50-75m for rimfire calibers and 150m for centerfire calibers.

      It doesn’t mean you can’t use them at longer distances. You just have to really watch your technique to keep everything consistent.

      I used a Leupold M8 scout scope (2.5×28) at 300m on a M48 8mm Mauser (200g FNM) and in single -snap engagement kept the 10 shots in a group covered by a single 2″ square spotting disc.

  3. Good info, was actually wondering about this the other day while comparing SWFA SS scopes with or without side parallax adjustment…

  4. That Sig scope looks great, I always get scared of the bigger knobbed / aggressively textured knobbed scopes snagging on every darn thing (when it isn’t sitting in a case or bench-or-other rest). What say you?

  5. Great analogy with the thumb Jeremy.
    This should help newbies get better groups with their rifles.
    Just picked up a new leupold LRP for one of my hunting rifles. They just have dots instead of yardage on the prarllax knob.

    • Definitely, I feel like I understand parallax adjustment for the first time (after shooting for 40 years). Have to admit I was side-focusing on my 4×16…

  6. And now for the corollary question to this article: how much inaccuracy does a scope with fixed parallax typically contribute to a decent shooter?

    Countless people have decent $250 scopes with fixed parallax. What does that mean for a person with good fundamentals who takes their time shooting at 100 yards at a range? Can they realistically expect no better than 2 MOA groups?

    • Too many variables to know. Fixed parallax scopes are often set to be parallax-free at 100 yards. But regardless, it’ll depend on a combo of the scope’s actual amount of error at a given range plus how much the shooter’s eye moves around. If you shot a group without ever breaking your cheek weld at all, you may have awesome results even if there’s technically a huge amount of parallax error in the scope. It’s a combo of scope error and eye movement…if you don’t have any of either one of those things, the other doesn’t matter.

    • At just the right distance from your ocular lens your eye will see a bright perfect circle with the target and reticle. Too close to the lens and you lose the circle. Too far away and you get a black ring around your view that closes in around your field of view. You can use this ring to correct parallax on a fixed parallax optic at longer ranges. Simply pull your head back away from the ocular lens until you get the black ring. Then try to keep your head fixed in a way that ensures the black ring has the same thickness on the top, bottom, left, and right. Doing this ensures your eye, your reticle, and your target is on the same axis (I.E. No parallax).

      • Anonymous,

        Thank you for the explanation of moving my eye farther back from the scope and keeping the black ring the same thickness on all sides. I had heard that from another source and have been trying to do that. It is nice to hear that from you and exactly why that is helpful.

  7. Yup. Just recently figured this out. Had a 200-yard session that was producing groups WAY worse than I knew I could shoot. I was perplexed. I made sure the scope wasn’t loose. A friend suggested maybe the gas block came loose. Nope. Later, I figured out that I had forgotten to adjust the parallax. It was set at 100-yards. DUH!

    I went back to the 200 yard range and made sure the parallax was set correctly. Groups tightened right back up!

  8. I had a Trijicon TA01 NSN that I bought at a gun show, supposedly new, around $1100. when I actually used it I found out that when you move your head up or down, the horizontal crosshair slanted one way or the other. drove me nuts.

    there is no parallax adjustment on a TA01, so I sent it in to the factory and they returned it saying it had some sort of issue with an internal shim, which they fixed… and it still did the same thing.

    is that related to parallax somehow? is it normal? do they all do that?

    http://static.bhphoto.com/images/images345x345/Trijicon_TA01NSN_4x32_ACOG_Riflescope_548760.jpg

    • when I actually used it I found out that when you move your head up or down, the horizontal crosshair slanted one way or the other. drove me nuts.

      Distance to target??

      If the target is 100 yards or more, it shouldn’t be doing this. Your eyes will focus at a target a 100 yards away and if you move your head around behind the optic the reticle should more or less stay perfectly on the target when your head moves around.

      If the distance is 10 feet in your office and your eyes are focused on a target 10 feet away and you move your head ever so slightly behind the optic, the reticle will wildly move all over the place and all over and off the target. And this is because your eyes are focused at something 10 feet away. Any red dot will also suffer from this. On an optic with fixed parallax, the reticle will be flat, sharp, clear, and unmoving with your target at the range the parallax correction is set. So if you are looking through it at very short ranges in your home or office, don’t let that fool you. Take it outside, look at something say 100 yards off and you will see the difference. These optics are designed for things far off, not up close.

  9. great article…very informative…maybe the best ive seen yet on ttag

    how about a follow up article on the ins and outs and secrets of cheek weld as it pertains to precision shooting

  10. I don’t understand what people are saying with “side focusing.”

    On my scope and for a target some distance away. I just simply adjust the focus of the scope until the target is clear. Without adjusting my side parallax, the target is perfectly clear and the reticle is blurry. I then (while focusing with my eyes on the clear target and NOT the reticle, I adjust the side parallax until the reticle is also sharp and clear alongside the target. At this point, both are in almost perfect focus and sharp and clear and nothing seems to move around when I move my head around.

    I thought this is what everyone else was doing.

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