09-11-2013, 08:51 AM
My understanding of the parallax adjustment is so the shooter can co-witness the focal plane of the target with the focal plane of the reticle. If your eye is exactly centred in the scope for every shot then parallax is not an issue because the light coming from the target through the reticle into your eye is exactly straight. Keeping your eye dead centre is a difficult ask however so manufacturers allow us to adjust the planes which when coincidental eliminates the distortion of the reticle relative to the target. Your eye can then be off-centre and yet the reticle does not 'move'.
Scopes designed for close ranges do not have expensive parallax adjustments and it aids speed. Parallax is fixed in the factory at a range where it is likely to cause the least amount of missing the target. It will be about the 130yard mark. Ever noticed the distortion in a fixed parralax scope when looking at a 50yd or even 25yd target? At closer ranges the parallax distortion will have less effect on accuracy than at longer ranges, hence the 130yd bias. Scopes designed for .22's will be parallax fixed around the 50yd mark.
Your noticing gross movement with the 'head-jiggle-test' at low magnification is because the parallax was way out relative to what you were looking at. The amount of shift is predicated by the diference between the focal planes, not the magnification. At higher magnifications this shift is more obvious.
Scopes designed for close ranges do not have expensive parallax adjustments and it aids speed. Parallax is fixed in the factory at a range where it is likely to cause the least amount of missing the target. It will be about the 130yard mark. Ever noticed the distortion in a fixed parralax scope when looking at a 50yd or even 25yd target? At closer ranges the parallax distortion will have less effect on accuracy than at longer ranges, hence the 130yd bias. Scopes designed for .22's will be parallax fixed around the 50yd mark.
Your noticing gross movement with the 'head-jiggle-test' at low magnification is because the parallax was way out relative to what you were looking at. The amount of shift is predicated by the diference between the focal planes, not the magnification. At higher magnifications this shift is more obvious.