Here’s another trick for lenses that focus by twisting a ring: focus on the nearest point you want in focus, then twist the ring on the furthest point you want in focus, then twist back to half way between the two. Then the near and far points will be equally out-of-focus.
The trick works on any camera where the focusing is by racking the lens in and out, and the mechanism for doing that is linear.
Where the focusing mechanism changes relative positions of lens elements, the trick may be less accurate.