Parallax and Its Effect on Precision

Parallax occurs when the target image and the reticle are not in exactly the same focal plane inside the scope. When this happens, lateral movement of your eye causes the reticle to appear to shift against the target — even if both appear sharp enough to see. The reticle is pointing at different spots depending on where your eye is.

This is not eye relief (how far your eye is from the lens) and it is not blur. It is a geometric misalignment. A parallax-free scope at a given distance means the reticle and the target image are co-planar — the reticle appears fixed on the same spot regardless of small head movements.

Get in position, aim at the target, and while watching the reticle, deliberately move your head a few millimeters left, then right, without moving the rifle. If the reticle appears to drift on the target, you have uncorrected parallax at that distance.

Adjust the parallax knob (AO ring on the front objective, or side-focus turret) slowly in one direction while repeating the head-movement test. Stop when the reticle no longer moves relative to the target as your head shifts. That is parallax-free for this distance.

The distance markings on the knob are a rough guide only — they are often inaccurate by 20–50 yards. Always trust the test, not the number.

Adjustable objective (AO): a ring on the front objective bell. Requires removing your hand from the stock to adjust — disruptive in position. Side-focus: a turret on the left of the scope body, reachable without breaking position. Side-focus is preferred for field work and bench sessions where you repeatedly change distance.

At what distances does it matter? At 100 yards with an average production scope set to 100 yards, the error may be under 0.5 inches — small but real. At 500 yards, with a scope set to a wrong distance and sloppy eye position, the error can exceed several inches. Always check parallax before a precision string, especially if you changed distances from your last session.