View Thread : HoKay, Teach Me About Parallax


Grump
We'll discuss repeatability and reliability of reticle adjustments later.*

I'm calling Tasco about the AO on one scope still showing reticle movement at something past the "infinity" setting, and more apparent movement horizontally than vertically. OK, it *is* a $150 or so scope bought on discount, but...come on!

Then there's the old Weaver 3x9x40 I've sent back for repair twice. First one was the plastic zoom tit crumbled (the one that travels in that 180-degree cut in the scope tube). THEN one of the crosshairs broke and I also asked for the parallax to be taken out. Checked it on the prior trip, and its parallax is maybe a half inch, again more horizontal than vertical, but with a big jump to something bigger as I move my eye past about halfway towards the image-loss point.

Both of these are variables, and both of them have the crosshairs moving with the eye movement--move right and the crosshairs move right.

What direction does which lens go when adjusting parallax from moving with towards zero and then moving opposite the direction of eye displacement? The design of the AO scope makes it hard to tell, but it *looks* like going out or away from the ocular lens moves it from being "close" to "far"

I'd like to understand the optical physics of the system, so to speak. I do grasp the foundational element of placing the reticle on a focal plane.




*Last time I was out, I used an AO scope which STILL appeared to have about 1/2-inch parallax at 100 yds, fired a 1-inch group (.308 reloads) outside the center square, put 5 or 6 clicks left on, fired one shot called 1/2-inch left into the center of the bull, and then dropped the remaining 4 shots inside the first group. 9 shots in just under an inch....

457ciSBC
Grump

What direction does which lens go when adjusting parallax from moving with towards zero and then moving opposite the direction of eye displacement?


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

Grump
Thanks. Looks like my objective elements remain too close to the reticle on the AO scope as well as on the older Weaver.

LR1955
Thanks. Looks like my objective elements remain too close to the reticle on the AO scope as well as on the older Weaver.

Grump:

Don't worry what the setting indicates. Adjust it until the reticule no longer moves when your head moves.

LR1955

Grump
Oh, I never did worry about whether the markings were calibrated.

I AM worried that when adjusting the parallax out, the error gets smaller and smaller and then a small portion remains after I've run out of adjustment...at 100 yards!

LR1955
Oh, I never did worry about whether the markings were calibrated. I AM worried that when adjusting the parallax out, the error gets smaller and smaller and then a small portion remains after I've run out of adjustment...at 100 yards!

Grump:

OK, if the movement is getting smaller or larger when you adjust the focus, then the system is working properly which implies too much or too little adjustment.

However, I believe that you may find this movement if your ocular lens is out of adjustment so if you haven't done so, check your ocular lens. After that I would attribute it to the mechanical quality of the optic.

One other thing. Generally a shooter will assume the right eye relief with the eye centered very consistently behind the optic. This tends to eliminate minor parallax problems. If, on the other hand, you are deliberately trying to cause parallax issues then you will see the results and in all likelyhood it is nothing that a optic manufacturer can do anything about.

Unless your optics aren't tracking -- I doubt there is anything wrong with them. Perhaps the issue is simply one of degrees of precision in terms of manufacture?

LR1955

Grump
???
LR1955:

Crowding or going long on your eye position will affect the parallax?

With the Weaver, I *did* get a few barely-good groups at the end of the shooting session by crowding in and centering my eye by centering the 1/4-1/3 field of view circle inside the black can'tseenuttin' ring as seen inside the ocular.

Coupla weeks ago, my oldest and I had a few laughs at the local gunshop looking at an $89.00 BSA variable with AO. There was no way it could come even close to eliminating parallax at 200 yards no matter how we adjusted it. I had given up on BSAs about 4 years earlier after looking through their $30 fatbody reflex scope. When moving my eye towards the side that has the red dot generator, the dot suddenly jumped about a FOOT compared to the building across the street at maybe 125 yards. Before that, it was wobbling "only" 4 inches or so.

LR1955
Crowding or going long on your eye position will affect the parallax?

Grump:

They will if your eye isn't centered. That being said -- note that I have stated that the visual perception of a human being is extremely good and thus if you think your eye is centered -- it probably is.

I trust that you are placing your eye the right distance from the ocular lens as your eyes would tell your brain to move closer to or farther from the ocular lens if needed.

I also advise you to check your ocular lens adjustment to ensure the cross hairs are clear to your eye when your eye is the right distance from the ocular lens. I am not sure that the cheaper optics make up for radical changes in eye relief.

Just my opinions though.

LR1955