Focus clutch
1 2 3 4 5 6 7 8

Focus clutch

Like the 10-25mm F1.7, the 25-50mm has a focus clutch mechanism. When you pull the focus ring back, a marked distance scale is revealed. This engages manual focus and also switches the ring's behavior from being speed-sensitive to offering a linear response (turning to a specific point always puts the focus at a specific distance).

Like nearly all autofocus lenses for mirrorless cameras, the 25-50mm lens is fully focus-by-wire, even when the focus ring is in its manual/linear position, but it behaves exactly as you would expect a mechanically-coupled lens to work, so it should present few surprises in this respect.

However, while the lens exhibits very little breathing as you refocus, it's not a parfocal design. This means that while you can refocus without significantly changing the framing of your shot, zooming in or out will require you to refocus the lens.