Just See — Don’t Focus
"But,” you say, “the sight is sharper when I close one eye.” We’re binocular creatures. Closing an eye has several disadvantages. It decreases your field of view, and you lose depth perception. The open eye dilates to gather additional light, attempting to compensate. And while the sight may initially be crisp, it won’t be for long. The open eye will fatigue quickly.
A better way to think about “focus” is to just “watch,” “look at,” or “see” the front sight naturally with both eyes open. The eyes are focused at the distance where the front sight is located. The sight may not be crisp or clear, especially as you age. How crisp you can see it isn’t the question. What counts is you’re looking at the front sight, as opposed to bouncing back and forth between it and the target.
It’s easy, too. Pretend you’re holding a pistol, except hold your thumb up — that’s your front sight. Pick out a target, and look at it keeping both eyes open. Raise your arm — keeping both eyes open — bringing the “sight” up into alignment between your eyes and target. Now — still with both eyes open — look at your thumb. There it is, front sight focus. It’s that simple.