Lens centering quality refers to how evenly a lens performs in all directions away from the image center. In a well-centered lens, sharpness and focus behavior are symmetrical around the frame. If the lens is decentered, one side or corner may appear softer or focus differently than the opposite side, even at the same distance from the center.

In practice, reviewers use the term when checking whether resolution changes uniformly along different radial paths from the center. A perfectly centered lens can still get softer toward the edges, but it should do so evenly. Poor centering means the optical elements are not aligned ideally, causing uneven sharpness.

So the main factor is optical alignment of the lens elements. A simple way to check is to photograph a test target with repeated high-contrast details arranged around the frame and compare sharpness in opposite directions or corners.