parallax adjustment

[jd45]

Hello to all, I would like to understand what this feature on the front of a scope does. Would someone enlighten me? Thanx for the feedback. jd45.

[PA-Joe]

It focuses the eyes on the target. The rear adjustment focuses the eye on the hairs.

[Iowegan]

Place your rifle in a vise or cleaning jig where it can be aimed down range, hands off.  Adjust position until crosshairs are dead on a target at 50 yds.  Look through the scope and move your head around.  Parallax is evident when the crosshairs appear to move on the target when the rifle is stationary and your eye moves.  All scopes have some parallax, however it becomes more evident at 9X and above.  The more powerful the scope, the more parallax you will experience.  This is bad because you must have the same exact hold and view for each shot to keep the rifle on target.  Many scopes above 9X have a parallax correction ring on the objective lens that is calibrated in yards/meters.  If your target is at 200 yds, make sure the ring is set for 200 yds, otherwise you will still get parallax.  This will keep you busy when varmint hunting.  Many shooters think their rifle shoots bad groups when the blame is really on scope parallax.

[gunnut69]

Paralex is the focus on the target.  That is how close the reticle and the target are to being on the same focal plane.  The focus ring on the eyepiece adjusts the clarity of the view for the users eye.  Also the marks as to yardage on the paralexx adjustment are pretty much just a suggestion..  Try a few out once to see how far off they can be..

[Iowegan]

gunnut69, Parallax is much more than a focus. If you use your AO ring to adjust distant target focus, you really aren't getting the true parallax correction. Yes, adjusting the ring does effect focus but that is a side issue. Parallax correction is optimized when the gun and target are stationary and your moving eye can not detect cross hair movement on the target.

I've found the AO ring calibrations on Leupolds, Burris, and other higher quality scopes track very close. On cheapies, not always the case. By the way, the parallax yardage marks are calibrated when the scope is set for max power. The rear focus ring plays a big part in how the parallax tracks. If your focus ring is set for your eye (which it should be) the distant target and cross hairs should be nice and clear. If your eye happens to be a diopter or two off, the internal parallax may not track properly.  The best way to focus a scope is to set up a target at 100 yds, set the parallax ring for the same distance, then adjust the rear focus ring. Parallax will then track with focus at other distances unless your eye is too many diopters off.

All scopes over 1 power have some parallax. Fixed power and variables without an AO are preset at the factory for 100 to 150 yards, with 150 being the norm. The exception is rimfire scopes where the parallax is corrected for 50 yards. The more powerful the magnification, the more critical the parallax.  

With a 10X scope, the AO set to 200 yds, and the target at 100 yds, you can get up to + or - 2" cross hair drift by just moving your eye. This means a "one hole" gun could shoot a bad group just because the eye wasn't positioned exactly the same for each shot.

The closer the target, the more critical parallax gets.  If you set up a target at 50 yards and do the exercise in my previous post, your AO ring should be aligned at the 50 yard mark. If you have a scope without an AO, just try it at 50 yds. The cross hair drift can easily be + or - 6".