Assuming you understand the general concept of parallax error(if you don't this won't make much sense). Basically parallax error means that changing how you look through the scope changes the POA. It's a lot easier to demonstrate than it is to explain. All optics (even RDSs) have a potential for parallax error. It is not a question of eye relief, SFP or FFP, all have to deal with parallax which has nothing to do with a specific zoom setting.
When they say parallax set at x distance means that inside of that distance you're ostensibly "parallax free" (no matter where your eye looks through the scope, the POA doesn't change though not even a RDS is truly parallax free, only so little that it doesn't make a difference - the greater the magnification on a scope, the greater the issue of parallax). Beyond that distance you have to adjust the parallax (assuming your scope has that feature) to compensate. According to Scott at Liberty Optics, adjustable parallax is not really necessary on scopes less than 10x.
Practically speaking think of it as the focus ring on an SLR camera lens. It's set in distance delineations out to infinity. Once you've ranged the target, select that distance on your adjustable parallax/focus knob to minimize parallax error.
Last edited by Gutshot John; 10-04-09 at 01:34.
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