How to Use Adjustable Objective Rifle Scopes

Co-authored by Roger Judd

Last Updated: July 12, 2024 Approved

Adjustable Objective (AO) rifle scopes are designed to allow the shooter to focus on the target. There are three main advantages: The target is in-focus, being in-focus will eliminate parallax (movement of the point of aim when the shooter shifts the eye position), and the range information on the focus knob can be used for better aiming.

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^{[1]
X
Research source} Sighting-in can have been done preliminarily, but additional sighting-in will be desirable after following these steps:
There are two optical systems in a rifle scope. The objective (front lens) focuses the target image on the reticle (cross-hairs); the eyepiece (rear lens) focuses the eye on the reticle. ^{[2]
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Research source} The eyepiece must first be adjusted before any adjustment of the objective.

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Unscrew the lock ring a turn or two so that the eyepiece can be screwed in and out. ^{[3]
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Research source}
This will cause anything you actually look at that is close to be very blurry.
^{[4]
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Research source} At this stage, we are only interested in focusing the eyepiece on the reticle and not on any actual target. Screw the eyepiece in/out until the reticle is in sharp focus. This may take several tries with removing your eye from the eyepiece between tries to give it a rest.
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Research source} (This does not have to be more than just snug.)
Now that we have a clear image of the reticle, the distant target image can be focused on the reticle. In practice, you will think that you are focusing the image on your eye, but what is actually happening is that the image is being focused on the reticle. Most objectives focus by turning the front lens. Some focus by turning a knob on the side of the scope. In any case, the idea is to get a sharp image of the target. It will be easier to focus if you choose a target area with some contrasting texture such as wood grain - you will see the image "pop" into focus better on patterns than on large areas.
You should now be able to move your eye from side-to-side while the rifle stays still and the cross-hairs of the reticle should not move on the target. ^{[6]
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Research source} This means you have eliminated parallax from your scope system for this target. If the distance to the target changes, you only refocus the front objective (or side focus). You never touch the eyepiece adjustment unless your prescription changes, basically.

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How do I zero in a rifle scope?

Roger Judd
Firearms Instructor
Roger Judd is a Firearms Instructor based in Mesa, Arizona. Roger and his team at Concealed AZ have been teaching NRA, Arizona Concealed Carry, group and individual firearms training classes as well as promotional, corporate, TV & media machine gun events since 2008. As an NRA Instructor, Roger specializes in teaching people how to safely use rifles, pistols, and shotguns.

Roger Judd

Firearms Instructor

Expert Answer

First, start by setting up your target at a distance of 100 yards, and make sure that your rifle is on a stable platform to minimize movement and maintain accuracy. Fire a group of three to five shots at the center of the target to see where your rifle is currently hitting. Then, locate the adjustment knobs on the top and side of the rifle scope; these knobs typically allow for one-quarter minute of angle (MOA) adjustments, translating to about one-quarter inch at 100 yards. If your shots are hitting low, turn the top knob to move the reticle up, making four clicks for each inch you need to adjust. If your shots are hitting left or right, use the side knob, making four clicks for each inch of adjustment needed. After making these adjustments, fire another group of shots to check their placement and adjust accordingly to how your bullet hits.

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Question

Does the Norinco 3-9X40 scope with fixed objective lens need parallax adjustment for a 10 meter target with lower magnification if it is zeroed for 30 meters? If yes, then how can it be done?

Community Answer

A fixed objective lens scope has a parallax free distance. Changing magnification does not effect that parallax free distance. Changing that distance requires moving the objective lens in or out in the tube. If you do that yourself, you'll void any warranty and perhaps allow dust and moisture inside. Fogged scopes are useless.

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Should I be able to put on and use a rifle scope with A.O. on my muzzle loader without any problems?

Community Answer

Yes, although an A.O. is usually not necessary for muzzle loaders, because the shooting distance isn't long enough to require a scope with an A.O. Be sure when mounting the scope that the A.O. has clearance between it and the barrel of the muzzle loader.

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Tips

Lens shades can help a lot. Many scopes come with an objective shade that screws into the front of the scope. Various slip-on shades are available for the eyepiece.

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Keeping the lenses clean is important. Never use any paper product on a lens no matter how soft you think it is -- all paper contains silica (think sand). The best cloth is one that opticians sell or give when dispensing eyeglasses; it is a "silk" (same as for men's "silk" ties) that works incredibly well. A LensPen is also an excellent tool -- it comes with a brush to get rid of most dirt and a pad for the smudges.

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The manual that came with your scope will have this same information but may cover special cases that you will find for a particular scope.

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Warnings

Never assume a gun is unloaded -- check this before working on the gun.

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Use empty chamber indicators.

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Follow all firearm safety rules.

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Keep the gun pointing in a safe direction when possible.

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