How your eye affects a parallax-adjustable scope

by B.B. Pelletier

Lots of interest in this subject. I will do more on scopes, open sights and related topics in the future.

A repeatable cheek weld
Cyberskin, this is for you. We know that the relationship of the sighting eye to the sights is critical to either canceling or introducing parallax, but how do we ensure the same placement time after time? This is where the fit of the stock comes into play. When the U.S. Army used wood stocks with definite wrists, soldiers were taught to grip the stock with the hand their trigger finger is on in a certain way. That positioned the hand in the same place on the stock every time, and then the soldier was taught to place his cheek against the stock so it touched his hand. I’m right-handed, so I was taught to touch the upper heel of my palm (back of the thumb) with my cheek.

When we switched over to M16s, the wrist of the stock was straight and no one had figured out the hold yet. I bet it has since been determined, but I don’t know what it is. Now, if you have a poorly fitted stock, as over 50 percent of them are these days (especially for using scopes!), there is an artificial way to ensure cheek placement. Figure out where you like to hold your cheek, then put a piece of tape on the stock at that spot. Every time you mount the rifle, put your cheek against that tape in the same way, and you will have solved the problem. Remember, cheek placement doesn’t have to be perfect – in fact there is no perfect way to do it. It just has to be consistent.

On to the eyes!
All good scopes have an eyebell (ocular) adjustment to correct for individual vision problems. The instructions on how to adjust this focus ring are in the owner’s pamphlet. If you’re like me, you seldom read those things. Still, this is a critical step to getting the greatest precision from your scope – especially when it comes to parallax adjustment.

The eyebell adjustment is actually there to focus the scope on the reticle, so it appears sharp. Adjust it by looking through the scope at a blank, light-colored surface, such as a wall, and turn the adjustment ring until the reticle lines are in sharp focus. When you do this, look through the scope for only a few seconds; because, if you continue to stare, your brain will take over and focus the reticle for you. Just keep glancing though the scope for brief periods and turning the eyebell adjustment ring until the reticle is sharp.

How this works
You wouldn’t think this adjustment has anything to do with parallax adjustment, and it doesn’t – directly. But, indirectly, it has a tremendous affect! If your scope is not adjusted before you start shooting, every parallax adjustment you make will attempt to sharpen both the target AND the reticle. Since it is impossible to do both (they are in two different planes), you will tend to average the adjustment – to vary it so the target and the reticle both appear to be in the best relative focus. That will leave the target somewhat fuzzy, and there is no way you can guess at the amount of fuzziness on repeated tries.

Let me put this another way. If the reticle is out of focus, it will appear to be the most out of focus when the target is in sharp focus. In extreme cases, it may disappear altogether. So without thinking, you will back off on the parallax adjustment until the reticle appears somewhat clear again. And that is what throws off your ability to determine range using the parallax adjustment ring or knob.

Don’t loan your gun!
The first thing a knowledgeable shooter does when borrowing a strange scope is adjust the eyebell to sharpen the reticle. When they give the gun back it’s out of whack for the owner. It’s easy to adjust it back, but how many shooters know to do it?

Let me tell you another horror story. I was displaying my field target rifle at an airgun show. A man picked it up and, without looking through the scope, began spinning the reticle knobs to feel the clicks. I hadn’t bothered to zero the knobs or to note their settings and I had spent an hour optically centering the reticle. In a few seconds, all that work was undone. People who do things like that are called “knobdickers” and they exist in great numbers. So – don’t loan your rifle, or be prepared for the consequences if you do!

27 thoughts on “How your eye affects a parallax-adjustable scope

  1. Wow, how did you not just beat the guy right there? What did you do?

    I guess thats what the zero-locking feature on all the leapers scopes is for. Well, I’m glad I have that now. 😀

  2. “Grass never grew there again” … hmmm, what kind of grass did they grow in concrete on the rest of that arena floor ? LOL Yeah, B.B., you should have called that guy outside and rezero’d your scope with his knobs and d**k as targets. As for M-16 cheek weld, in 84 in basic my drills taught us to put the tips of our noses against the charging handle, which many of us were at first very afraid to do, lest the expected recoil crunch it … until we got used to there being almost zero recoil (felt, anyway), thanks to the buffer assembly in the buttstock.

  3. Great post B.B. These posts on scopes are always very helpful. On a related topic, I was wondering how in the world you use a scope if you’re right handed, but your left eye is dominant. I think this may be the case with me, but I haven’t found a good way to use the left eye, I just use my right. I wear glasses and the other thing I’ve noticed is that if I’m not looking right through the center of the lens of the glasses, I get distortion and can’t see the target as well. Any suggestions here?


  4. Left eye,

    You could always teach yourself to shoot left handed. My dad has always done that, and he’s right handed. He says he can hold the gun sturdier because his right arm is stronger. Just a thought.


  5. Field Targieter,

    If you still havent bought the WE Hi Capa, I would advise against it. The Tokyo Marui version is much better quality and durability wise as the WE’s metal slide is too heavy and creates sluggish recoil and blowback unit problems. This isnt the case with the TM gun though.

  6. Hi! BB,
    Thanks for your post of “the best airgun” under $100.00. How about a short list of the best .22 air pistol and rifle under $200.00
    Thanks & regards,

  7. Left eye,

    I have the same problem, being lefthanded with a dominant right eye.
    I think lama’s idea is not that bad, I tried shooting right handed, and got very good groupings! It seems true that the stronger hand being in front does help with holding the rifle steady. It’s just gonna take some time to figure out a new spotweld and all the diffirent positions!

    On a diffirent note, I have been wondering about something. To improve the lock time of a springer, would it not make sense to reduce the weight of all moving parts, ie the piston and tophat. IMO, the lighter the moving parts, the quicker the reaction! But I haven’t come across anyone who has done it, so there must be a good reason why this is not done. Hoping you could shed some light on it.


  8. There’s an optical affect that I’ve noticed when using diopter sights, but I’m not sure of whether it’s a parallax affect.

    When my eye is off-center relative to the alignment of the rear iris to the front sight, the front aperture ring appears distorted, as though the ring is thicker in a given region. I can correct this by canting the rifle towards my face a bit, or correcting my cheek position. It seems that the distortion appears on region of the aperture ring in the direction of my eye’s misalignment to the sights. For instance, if my eye is positioned too low, the lower edge of the ring is magnified.

    Is this parallax or some other optical affect?

  9. Left eye If you haven’t seen a eye care specialist in a while it may be a good idea. I had a cataract removed that was from birth. Guess what one of the complications up to a year is? Retinal Detachment if untreated is a 100% chance on going blind in that eye. Not saying thats what you have. Like the others have said try shooting lefty , thats what I do. Not a hard decision for me to make ,and I’m pretty good at it.
    There is so much good information here its going to take some time to engrave it in my head. Thanks B.B. , Matt, Mr-Lama and others for sharing links and information.

    B.B one question do people in field target adjust there scopes turrets for targets at different ranges , knowing that it may take a few shots to settle down ,or do they use there mil dots to determine the point of impact?

  10. B.B.–When I had my scope mounted I did not remove my front site. During several trips shooting I would notice a faint circle showing up when I looked thru the scope–I finally realized it was the hood on my front site-(rws 350). Qther than being an annoyance from time to time could this throw of the accuracy of my gun? Thanks -Scott

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