Benefits of A Side Focus Adjustment on a Riflescope

The benefits of a side focus adjustment on a rifle scope come into play when using either a high magnification scope or shooting drastically different yardages with the same scope.

Parallax, derived from the Greek word parallaxis (which means “alternation”), is the difference in the apparent position of an object viewed along two different lines of sight. It is a term often heard in the world of rifle scopes, but what does it mean?

Simply put, parallax is the apparent movement of the reticle (crosshairs) on the target when the shooter’s eye moves off-center from the scope’s optical axis. This misalignment can cause errors in shot placement, especially at longer ranges. Parallax can be eliminated or greatly reduced through the use of parallax adjustment knobs or side focus dials that adjust the internal lenses to ensure that the reticle remains in the same position relative to the target, no matter where the shooter’s eye is positioned. Understanding how to properly adjust for parallax is crucial for achieving accurate and consistent shots, particularly in precision shooting situations.

An Analogy on Parallax

Remember the dial-like speedometers in cars. Think about it being observed by the driver and the passenger of a vehicle at the same time. The driver, looking directly at the needle in relation to the numbers on the back plate, will get a more accurate reading than someone in the passenger’s seat viewing the needle at an angle. Think of the needle as the reticle and the back plate as the target. Adjusting the side focus to correspond with the distance to the target eliminates parallax at that distance.

One thing to note is that if you are looking through the optical center of the scope, parallax does not show up. It is only visible when your eye is off center. You may not be looking through the optical center of the scope if you’re shooting at sharp up or downhill angles. It will also affect you if your head is not positioned on the firearm’s stock properly.

Identifying Parallax

The greater the distance to the target and the higher magnification of the optic means more parallax error.

While keeping the rifle still and looking through the riflescope, a slight nod of the head up and down will quickly determine if parallax is present. To remove it, start with the side focus mechanism on the number matching the distance you are shooting, then rotate in both directions, stopping when you see the target in focus. Note the reticle should already be in focus if you adjusted (link) the quick focus eyepiece properly. A common mistake is thinking the side knob will focus the reticle.

Josh at Pursuit of Accuracy shows you how to shoot better groups by utilizing your side focus adjustment.

Benefits of a Side Focus Adjustment

A side focus adjustment on a rifle scope has numerous benefits for shooters, particularly those who engage in long-range shooting or hunting. This feature allows the shooter to adjust for parallax without having to change the position of their head or body, which can be especially useful in difficult shooting positions or when shooting from a prone position. Additionally, side focus dials provide precise adjustments that allow the shooter to fine-tune the focus of the reticle at different ranges, ensuring that shots are consistently accurate. Another advantage of side focus adjustment is that it allows for easier and quicker adjustments when switching between targets at different distances. Overall, a side focus adjustment on a rifle scope is a valuable feature that can greatly enhance accuracy and improve a shooter’s overall performance.

Generally speaking, parallax should not be a major concern for the average big game hunter. If your scope happens to have an adjustment for parallax and you don’t have a need for it, you can set it at 100 and never touch it again. Keep in mind that the yardage markings on the parallax adjustment are not exact and are just meant to get you in the ball park. Fine tuning will need to be done to further eliminate parallax. Parallax correction is a must for anyone attempting to use either a high magnification scope or shoot drastically different yardages with the same scope.

To learn more about the benefits of a side focus adjustment, check out this video from co-founder Jon LaCorte.