Interesting answers, hoping to get more.
At the age I've now reached, actually at the age my eyes have now reached, getting a scope to focus and be clear can be a challenge. When fast focus became available I was surprised how well my eyes liked it. It was to the point that the older Leupolds would not focus clearly for me at close range even with the parallax set at 50yds. For what ever reason, the fast focus scopes worked in that regard. Why some of the optic companies rimfire adjustable objectives are only going down to 50yds. is beyond me when they used to go down to 10yds. That is one of the many reasons I like the Tract 4-12X40 AO scope and the old Burris 6X mini AO's.
As Jim in Idaho brought up, I have changed the parallax on several fixed parallax scopes. The hardest part is getting some of the outer rings to break loose.
