what is parallax?

[yotechoker]

If a scope is parallax free at 100yds, does that mean it is distorted at less than that? Is a 50 yd parallax better? 

[RodBuster]

Parrallex is the shift of the reticle in comparison to the target when your eye moves off center. I don't think it has anything to do with distortion of the image.

If you are precision shooting at ranges less than 100 yards, then you would be better off with a scope adjusted to a parallex of that range.

AO scopes can be adjusted for a wide range of yardages.

To experience what parralex is, line up your crosshairs on something with the rifle on the bench. Then, without touching the rifle, move your eye off center. Movement of the crosshairs will occur at any range other than that which the parralex is set for.

[Keith L]

Paralax becomes an issue for shooters when they either have inconsistent cheek weld or they mount the gun differently each time.  Any distance other than the one the scope is corrected for will have a different point of impact for different places you look through the scope.  The amount of change depends largely on the distance: the further away the target the more the change in poi.

For .22s a 50 yard paralax correction is better than 100, since (I know I will have many disagree with this but) a .22 is intended to be a 50 yard or so gun.  Most centerfire scopes correct at 100 yards since that seems to be the most desirable range for them.  17 HMRs are a legit 100 yard gun as well.  .22 mags may be, depending on the ammo, in my experience.

As Rodbuster said, the best option is a scope with AO (adjustable objective).  Then you can set the scope for any distance from close up to infinity.

Good luck with this.

[yotechoker]

Good stuff, thank-you

[majorKAP]

Parallax error is an optical aberration of telescopic sights in which the point of impact can vary with eye placement.  It is caused by the fact that the target does not fall on the same optical plane as the reticle. It is of primary concern for very precise shooting, such as shooting for group.  Most fixed focus hunting scopes are focused at about 150 yards so if your target is at a different range you can get parallax error if your eye is not centered in the cone of vision consistently. 

Maximum parallax error occurs when your eye is at the very edge of the exit pupil and for a 4x hunting scope focused for 150 yards the maximum error would be about 1" at at 500 yards if your eye was fully off center--giving the possibility of a 2 inch combined error if your eye placement varied from side to side of the field of vision.  At short distances the 4x scope above would have about 2/10" error (4/10" total combined error) at  100 yards.  Thus parallax error is primarily a worry for shooting groups but not in the field.

Some scopes have an adjustable objective lens that will allow you to adjust the plane of focus to your target's approximate distance thus minimizing parallax error.  If your scope does not have parallax adjustment it is important to consistently place your eye in relation to the scope.

Typically, non adjustable scopes are set for the following parallax free ranges.  Consult your owner's manual to verify this data for your scope.

    Rifle scopes - 150 yards
    Handgun scopes - 100 yards
    Shotgun scopes - 75 yards
    Rimfire scopes - 60 yards

Taken from http://frfrogspad.com/index.htm

[victorcharlie]

Parallax, or more accurately motion parallax (Greek: παραλλαγή (parallagé) = alteration) is the change of angular position of two stationary points relative to each other as seen by an observer, due to the motion of an observer. Simply put, it is the apparent shift of an object against a background due to a change in observer position.

There is a fairly good write up one it here:

http://en.wikipedia.org/wiki/Parallax

[yotechoker]

I believe I just got a few credit hrs worth of physics!!  Thanks! (it'll take a while to digest that...)LOL