If the fast focus ring on the scope is to adjust parallax, what is it for with AO or a side parallax adjustable scope? I believe the fast focus ring is to adjust picture clarity not parallax. Thoughts? Optik1

I'm assuming when you say fast focus ring, you're talking about the one on the eyepiece, correct?

If so, that focus is for the reticle, not parallax. The AO/side focus is for parallax correction. Those scopes without it are generally set parallax free at the factory for 150 yds or so.

IIRC typical parallax is set at 150 yds but shotgun and 22rf is set at 75 yds. Of course the 22rf and shotgun are normally shot within the shorter range.

The twiddle-able eye-piece reticle focus would seem unnecessary since most of us only need to fix it once. However, some Europeans assert that our focus changes in very poor light such at dusk and later. I can verify noticing this - after I had taped up the eyepiece against water intrusion.