The adjustable ocular ring is for fine-tuning the focus of the reticle only, not the image. The A.O. adjustment, in addition to eliminating parallax error at various ranges, adjusts the focus of the image. Using it to determine range is viable only if you check its markings against known distances beforehand, and maybe put your own markings on the distance scale/ring, since they are not at all accurate. Also, at long distances, you can move the ring a fair bit without seeing a huge difference in focus.
Parallax is not going to introduce any aiming error at all if your head is centered properly behind the ocular lens. It only comes into play if you move your head around from shot to shot. So don't.
John
Parallax is not going to introduce any aiming error at all if your head is centered properly behind the ocular lens. It only comes into play if you move your head around from shot to shot. So don't.
John