Home Forums Hunting & Shooting Hunting Optics Parallax Question

The latter. I see it when I am am cozying up to my stock and getting settled in. I don't understand what happens in the scope when a fixed parallax scope has the parallax adjusted from say 100 to 50 yards. Or when the parallax adjustment is moved through its range

The parallax adjustment mechanism positions the target image relative to the reticle image inside the optic. In a fixed parallax optic, the image of whatever is in the FOV at the distance parallax is set, will be in the same plane as the reticle image inside the optic.

The goal is to get the image of the reticle and the target on the same focal plane. Apparently, it can be done more than one way. This is why there are adjustable objectives (move the objective lens fore and aft), side focus (which does it with another lens, not the objective), and the SWFA fixed power scopes that have the parallax adjustment where most variable scopes have the magnification adjustment (yet another way to do it.)

Probably the easiest to understand is the adjustable objective, and I believe moving the objective fore and aft is how most scopes that are parallax free at only one distance are adjusted.

I don't understand optics well enough to know exactly how it works, much less try to explain it, and much, much less in easier to understand terms.

There is also the trick Dirtfarmer suggested, although that probably works well only on a bench.

Place an objective lens so that it casts an image on a ground glass. In line, place an ocular lens of shorter focal length behind the glass, so that the image on the ground glass is magnified. This is your basic two-lens telescope. While looking through the ocular, remove the ground glass. Nothing changes except that the image becomes more crisp as the texture of the ground glass goes away. The point is, the real image formed by the objective lens is still in the same plane in space, whether the ground glass is there or not.

If that real image in space is in the same plane as the reticle, there will be no parallax. If it's not in the same plane, the reticle will move with respect to the image as you move your eye left/right, up/down. The parallax adjustment on an adjustable objective scope allows you to move the real image forward and back, so that it's in the same plane as the reticle.

Is something we worry about more than necessary. Some quotes from a Leupold owners manual.

It is significantly worse than that at higher powers though - you can see this by moving your head around behind a rifle on bags, where there is a parallax error.

It can also get bad "up close", say 25 yards, if you are shooting very small targets with a .22 up close.