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Adjustable Objective (AO) lens

Fine focus in a flash

Tim
Tim
Scopes

Adjustable Objective (AO) lens

Table of Contents

Adjustable Objective (AO) lens scopes are a rifle scope that is becoming increasingly popular in Australia as well as overseas.

An adjustable objective is a feature that allows the shooter to fine-tune the focus of the reticle (crosshairs). This is especially useful when shooting at long ranges, where small changes in focus can make a big difference in the accuracy of the shot. Precision Rifle Shooting is a good example where an AO would be handy. Long ranges with limited time.

The adjustable objective lens is located on the front of the rifle scope, near the objective lens. It is usually marked with a range of distances, such as 10 meters or yards to infinity, and can be adjusted by turning a small knob, lever or a band housed on the objective bell housing.

Some AO scopes also have a parallax adjustment, which helps to eliminate the parallax error that can occur when the eyepiece and objective lens are not perfectly aligned.

Adjustable Objective Lens
Adjustable Objective Lens

Advantages

Some advantages of an AO scope are:

  • It allows the shooter to quickly and easily adjust the focus of the reticle without having to move their head or change their shooting position. This can be particularly useful in fast-moving situations, such as hunting or precision shooting, where the target may be moving or changing distance.
  • It allows the shooter to fine-tune the focus of the reticle for their specific shooting conditions. For example, if the shooter is using a heavy caliber rifle with a lot of recoil, they may need to adjust the focus of the reticle to compensate for the movement of the rifle during recoil. Similarly, if the shooter is shooting at long ranges, they may need to adjust the focus of the reticle to account for other factors that can affect the trajectory of the bullet.

Disadvantages

Some disadvantages of an AO scope are:

  • They can be more expensive than non-AO scopes, as the additional focusing mechanism adds to the cost of the scope.
  • Some shooters may find the AO knob or lever to be cumbersome or difficult to use, especially in fast-moving situations where quick adjustments are needed.
  • Added weight can be a consideration in some circumstances, particularly if you are lugging it around in the field hunting for long periods.

Adjustable Objective Scopes

Vortex Crossfire II 4-12×50 AO Rifle Scope
Vortex Crossfire II 4-12×50 AO Rifle Scope

Summary

Overall, an AO scope can be a useful tool for shooters who need to fine-tune the focus of their reticle for specific shooting conditions, or who want the ability to quickly and easily adjust the focus of the crosshair without changing their shooting position.

While they may be more expensive than non-AO scopes, they can provide a level of precision and versatility that is not available with other types of scopes.

FAQ (Frequently Asked Questions)

The adjustable objective (AO) allows adjusting the scope to be free of parallax error at different distances. Parallax is rarely an issue unless you are shooting over 200m (250 yards). When hunting this can be a drawback if you encounter targets that are closer than that. The AO is generally mounted on the Objective Lens Bell at the front of the scope, this means it is hard to reach when shooting. Therefore the AO scope tends to be used at fixed distances such as benchrest competitions. 

Photo Credits: Vortex

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