The lens zooms and focuses something very far away, yet the reticle inside the lens assembly is in perfect focus just like the far objects. How?
The image of the distant object is formed in the plane of the graticule.
The eyepiece is then focused on the image of the distant object and the graticule which is in the same plane.
The objective forms an inverted image of the distant object in its focal plane.
The next lens combination forms an erect image in the plane of the graticule (reticle in North America).
That image of the distant object and the graticule are focussed by the eyepiece so that the eye sees the distant object and the graticule both in focus.