Many average shooters who do most of their rifle shooting from a deer stand. They don't know what parallax is and could care less as long as their rifle hits what they shoot at. Those who have scopes with a parallax adjustment think it is a focus knob to clear up the sight picture.
This is because most shots taken by hunters are less than 100 yards and are taken at deer or similar size game. With targets this size, at this distance, parallax means little therefore the need to understand it and adjust correctly for it is not necessary.
Most target scopes for hunting or close range shooting are called "parallax free" which means there is no adjustment for parallax because it is set at the factory usually for around 75 to 150 yards. Great for close up shooting but when you intend to stretch out your distance, a parallax setting is required for maximum accuracy. So what is parallax?
Parallax is the error you see when the focal plane of the target and the reticle are not on the same plane. You will know you have this error when you can move your head while looking through the scope and the aim point on the reticle moves around on the target.
What causes scope parallax ?
The figure below helps to explain parallax error.
When parallax is not adjusted correctly, the aimpoint or center of the cross hairs will move around on the target as you move your head while looking through the scope. This is because even though the sight picture might be somewhat clear, the reticle and the target are not on the same plane.
This causes a minor error in your aim point up close but can be huge at 300-1000 yards. It can also cause misses at very small targets at close range.
When parallax is adjusted correctly there should be no movement of the reticle in relation to the target when you move your head.
Our goal of stretching the distance and accuracy capability of rifles to and beyond what's expected dictates that we use scopes with an adjustable paralllax that can go far beyond most standard factory offerings today.
Further understanding of parallax?
Parallax is an optical illusion that must be corrected for an accurate shot. You will usually see a dark shadow on one side or the other in the scope as you move your head around. This is normal but movement of the reticle is not.
A simple example is to hold your index finger in front of your dominant eye. Pretend it is your site and align it with an object a couple of feet in front of you. Close one eye and make sure your finger is aligned with the object you picked.
With the eye still closed, move your head to the right and left without moving your finger. Notice how your finger is no longer aligned with the target as your head moves. This is parallax. Your finger and the object are not on the same focal plane.
Now put your finger on the target you were aligned to. That's right, actually touch it. Now move your head around. The target stays aligned with your finger. That is because your sight (finger) is now on the same focal plane as the target.
Adjusting parallax is like moving your finger to the target to minimize error in what you see if your head moves.
Using a scope with a fixed parallax means that parallax is perfect at the range it was set up for but will be slightly off at distances that are further or closer. With hunting scopes this really doesn't matter much as the effect on accuracy will be minimal unless your are shooting at ultra long ranges or tiny little targets up very close.
Do I need parallax adjustment on my scope?
If you are a hunter and your primary targets are large game, and your longest range for taking a shot is 150 yards, then no, you don't need adjustable parallax on your scope.
Within this range you could even go with an optic that is classed as parallax free like a red dot. These optics are designed so that the point of impact will be where the dot is.
If you are a long range big bore shooter who takes shots beyond 300 yards, then yes, you absolutely need adjustable parallax on your scope. You would be hard pressed to find a quality scope for these rifles that comes without it.
Here are some of the best long range scopes I have found. I own all 4 of these and have fallen in love with the clarity and accuracy at ranges out to 700 yards. I don't have much of an opportunity to shoot further here in the Southeast.
These scopes all have side parallax adjustments as opposed to those located on the objective end of the scope. These allow easy adjustment while staying in a position where you can look through the scope. Shooting position does not need to be sacrificed.
How do you adjust parallax?
Your parallax adjustment knob will preferably be located opposite the windage adustment knob. It will have distances printed on it. You can get close by using these numbers but don't trust them completely. Everyone's eyesight is different and therefore eliminates perfect use of the these distances.
You will know when the setting is right when you are experiencing no "target creep" or your crosshairs don't appear to be moving on and off the target when you move your head slightly, assuming a good rest. The target should also appear to be crystal clear.
Keep in mind that the numbers on the parallax adjustment knob are just references and your eye may require them to be different from the distance indicated by the numbers. Use your eye, not the numbers.
Don't mix the terms parallax and focus. Focus or ocular adjustment, is an adjustment right in front of or on the eye piece of the scope. The sole purpose of this adjustment is to make the cross hairs crystal clear. It is best to adjust this against the sky or a single colored wall.
Adjustment of the ocular lense is what you are after here. See the ocular lense on the diagram above. The adjustment is usually just a ring around the ocular lense that can be locked down. Note: this adjustment is only for making the reticle clear to your eye.
Once adjusted so the reticle cross hairs are clear, and this is the only goal of this adjustment, lock it down. It is adjusted correctly for your eye and you shouldn't have to touch it again unless your eye sight gets worse.
Make this adjustment before taking shots or adjusting for parallax.
Parallax is completely different but when adjusted correctly it yields a target that is in focus. Now this statement also depends on depth of field for your scope but for our purposes, we don't want to complicate this discussion further.
Adjust parallax for a clear view of the target, if slight eye movement yields no "target creep" you have a good parallax adjustment. Take the shot.
Remember, what you perceive as perfect focus may be a little different than having parallax correct. The goal of parallax adjustment is to completely eliminate cross hair movement when your head moves. Clear focus with normal vision is a by product of a good parallax setting.
Shooting practices that can minimize error
One way to minimize the effect of parallax is to center your eye in the scope on every shot. Parallax adjustment can be slightly off but if your is centered in the eye piece it won't matter.
If you are seeing a black shadow around the edges of the scope, your eye is not centered in the scope. Some people intentionally back their head back away from the scope to avoid being hit in the forehead when the rifle is under recoil.
This is a bad habit and if you have to do this your scope is not positioned correctly. Your rifle doesn't fit. Adjust your scope until you are comfortable with not being hit when the rifle recoils but the position is natural for you and you don't see the black shadows.
This means your eye is in the center of the eyepiece and any error that remains in parallax will be minimized.
The best way to ensure correct eye position is with a good cheek weld on the stock. If scope rings are too high or the comb of the stock is too low getting a good cheek weld will be impossible.
You can correct a low stock comb with an adjustable cheek riser. I have these on most of my rifles because I want to make sure the all fit me the way they are supposed to. See the one I use here on Amazon.
If you have ever shot a bow, the first thing you learned was to anchor some part of your draw hand to some part of your face at full draw. For me, this was my index finger in the right corner of my mouth.
This insured my eye was properly aligned with the peep or rear sight on the string and as long as I did this the same way every time, my shooting was much more consistent, not by eliminating parallax but by making the error I saw the same on every shot. With this situation, sights can be adjusted for the error
The same principle applies with parallax when shooting a rifle. Your cheek weld, position of right and left hands on the stock, and pulling the trigger straight back to fire the shot are just a few of the techniques that must be consistent when shooting for accuracy.
Proper shooting technique is something we should all strive for but also realize, we are not robots. Counting on our techniques being perfect for every shot when in the field or even under a little stress is not realistic.
If you are a hunter whose average shot ranges 150 yards or less at deer size animals parallax is not a real concern for you. But if you like to stretch the capability of your rifle to it's limits and beyond, and strive for the perfection of hitting smaller and smaller targets, you must be able to adjust for parallax errors.
Setting the rifle up to fit you in order to promote correct shooting techniques is also necessary to keep your eye centered in the scope and stabilize the rifle.