Could someone please explain this to me as it relates to point of aim through a scope?

I realize what the definition of parallax is, but how does an adjustable parallax work and how is the best way to minimize parallax when shooting (besides the obvious-consistent noggin placement on the stock)?

Please keep this on topic. Thanks in advance.

PARALLAX ON 24HOURCAMPFIRE

Thanks. I saw some of those threads via my google fu, and it is great info but doesn't answer my question, though I haven't read them all in depth.
Maybe I haven't explained my question good enough though.

I am wondering how parallax adjustments in a scope work, not necessarily how to adjust for it. I can read how to do that in the first thread in your link. It seems to me keeping your head aligned as precisely as possible through the scope would minimize parallax, so I am unsure why any kind of setting or adjustment to the scope is necessary.

I also see a lot of parallax adjustment discussions pertaining to rimfires at 50 or 100 yards....at that distance what does it really matter?

Moves a lens for and aft I'd think.


https://www.6mmbr.com/parallax.html




http://rimfirebenchrest.com/articles/parallax.html

As eyes turn to a sleepy little burg in western Montana, anticipating the explaining by the knowledgeable explainer of things.

If on a bench, trying to shoot groups when parallax isn't perfect, one trick is to move your head back until all you can see is the target with minimal reticle showing.

That forces your head to be in the right place for the shot. Not for a big boomer or heavy kicking rifle.

DF

Methinks the dial thingy moves the lens thingy.

The adjustment moves a lens or lenses so the target image and reticle come into focus at the same place. That way you can't "look around the reticle" and see movement of the target.

Fine, get all technical.

I knew that "look around the reticle" would be too deep for some.

Focus may not be the correct term for it. You can have a clear image (ie focused) but still have parallax, and adjusting the focus affects the parallax to some extent. The Bushnell on my 22 has parallax adjustment and was the only scope I had where the range settings on the parallax adjustment actually matched the range. My eyes have gotten worse with age and I've had to adjust the focus, and now the parallax range setting doesn't correspond with the range. With most of my scopes I have to go for a parallax range setting greater than the actual range - I've got it noted somewhere what settings I have to use (I should mark it on the scopes.)

https://armament.com/sites/default/files/training/HowToParallax.pdf

The image from the objective falls on the focal plane of the reticle. "Focus" is used in terms of optical systems as well as your eyes. What you're calling "focused" to your eyes doesn't necessarily mean that the objective and reticle lens are focused on the same plane.

Yeah but the confusion arises when the scopes have both a focus adjustment and a separate parallax adjustment.

Ocular focus

And

Parallax focus

The ocular is properly focused when the reticle is sharp and clear. Adjusting parallax moves the entire image of everything in view to and fro. When the target of interest is in the same focal plane as the reticle, then the target and the reticle will be in the same plane, all in focus and without apparent parallax.

If you want to play around with some numbers, or set up your own spreadsheet to play around, there is a good technical article here:
http://www.rimfirebenchrest.com/articles/parallax.html

In general, the higher the magnification, the greater the parallax for a given deviation of your eye from the optical centerline. In other words, if your eye is 2 mm off the optical centerline, you will get more parallax at 9x than at 3x.
If a scope is set up to be parallax free at a "far" distance, usually 150 yards for a big game scope, this minimizes parallax at "really far" distances, say 400 yards. But it makes parallax worse "really close", such as 25 yards.

Now, this is relative. It is not difficult to get parallax errors of 1/2" at 25 yards with a typical big game scope at high power. 1/2" is nothing if you are shooting at most critters, even small ones. But if you have a $10 bet with your buddy that you can hit a penny at 25 yards with your .22 rimfire, that 1/2" can cost you some money!
Another way to look at it is that the parallax error is likely greater than the group size of a good .22 at 25 yards.

Yet another way to look at it is with .22's we often shoot at really small stuff pretty close. Even that close, we need some magnification. Now we have a good chance for parallax to give us trouble. So serious rimfire shooters tend to want parallax adjustment on their higher power scopes.

I have accepted that I will go to my grave with much of parallax remaining a mystery to me.

Are you saying you don't understand it from the point of view of experiencing it, or the more technical aspects of what causes it and how to get rid of it or mitigate its effects?

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.