I have a Weaver Classic Extreme 2.5-10 x 50 with side parallax adjustment. When set at 100yds the scope is focused and parallax free. The adjustment goes down to 50yds , but to eliminate parallax and be in focus at 50yds the knob has to be turned all the way up to infinity. Weaver said if it is good at 100yds there is nothing wrong with it . Can anyone enlighten me on what is going on ?