I'm not sure about the Pony specifically, but usually a front element focussing lens only has a single thread helical so it should only be able to be screwed on in one way. If not, then the focus ring probably has set screws, screw the lens in, loosen the screws, focus the lens on an object, get a tape measure and match the distance on the tape with the distance on the focus ring, and re-tighten set screws.