My scopes aren't adjustable for parallax, and the Leupold ones are nominally set to be parallax free at 150 yds. Is there a theoretical or practical maximum parallax error at 100 & 200 yds.?
Yes. the maximum parallax error E at a given target distance t for a scope which is parallax-free at distance p and has an objective lens diameter D is given by the equation
E = 0.5 D (abs(t-p))/p
So, for example, if you have a scope with a 40 mm objective lens, parallax free at 150 yards, maximum parallax error at 200 is
E= 0.5x40 (abs(200-150))/150
=6 2/3 mm
Similarly, for a target at 100
E= 0.5x40 (abs(100-150))/150
=6 2/3 mm
That is to say, if your eye position is at the edge of the exit pupil, you could be as much as 6 2/3 mm off at these distances, in these particular examples.
