parallax ?

R

rebs

New member
when mounting a scope on a AR 15 crry handle, I have heard it may have something to do with paralax. What is paralax ?
 
Put a straw into water in a clear glass.

Look through the glass at the straw.

Notice it looks like it is offset.

That is parallax.

When you bend light, you cause image distortion. When you have image distortion, what you are looking at isn't really where it seems to be.
 
For a simple answer - for a 22rf or shotgun scope parallax is set at 75 yds, For CF rifles it's set at 150 yds.
 
Man, I haven't posted here in years.

/puts on geek glasses

Crow Hunter, that is incorrect. What you're describing is refraction, no parallax. Refraction is what happens to light as it passes through different mediums (air, water, glass, etc).

Parallax is the difference in the appearance of a field of view between two different points of view. Close your left eye, hold your right thumb out in front of you and line it up on something like a telephone pole. Now close your right and and open your left, and you'll see that the telephone pole and your thumb are no longer lined up. That is parallax.

Refraction:

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

Parallax:

http://en.wikipedia.org/wiki/Parallax
 
In Astronomy terms, paralax is when your point of view movies and objects close to you moves a lot while things far away move only a little. The further the object is away from POV, the less paralax we observe it having.
 
In a riflescope, if you move your eye a bit from, say, centered on the scope to a little bit off-center and the crosshairs appear to move on the target, you're experiencing a problem with parallax.

Most scopes are pre-set. "AO" means an adjustable objective lens and is used to correct for parallax. It's commonly not a problem for pre-set scopes out beyond 100 yards or more.

If your scope is not adjusted for a particular range of distances and you don't have your eye in the same place for each and every shot, you won't get tight groups.

As mentioned above, scopes intended for .22 rimfire commonly are preset to shorter distances than scopes intended for centerfire.
 
Art Eatman claims:
Most scopes are pre-set. "AO" means an adjustable objective lens and is used to correct for parallax. It's commonly not a problem for pre-set scopes out beyond 100 yards or more.

If your scope is not adjusted for a particular range of distances and you don't have your eye in the same place for each and every shot, you won't get tight groups.
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Close, but not quite right.

Adjusting the objective lens only focuses the target image in the reticule plane. It does not technically correct for parallax because any object closer or further than the target will have parallax on the reticule.

Once the objective lens focuses the target on the reticule, you can move your eye all over the place and there won't be any parallax for anything at that range.
 
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Parallax is something far too many supposedly knowledgeable shooters worry about. Buy a decent scope, put it on, sight it in and shoot. If you miss it's your fault not a scope/parallax issue.

LK
 
Parallax is something far too many supposedly knowledgeable shooters worry about. Buy a decent scope, put it on, sight it in and shoot. If you miss it's your fault not a scope/parallax issue.
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That is not true and it is very misleading.

Parallax exists in optical systems when the crosshairs and the target are not in the same plane.

It is a SIGNIFICANT source of error and alignment of optical systems.

When you focus on a target, you should NOT see apparent movement of the target relative to the crosshairs when you shift your eye slightly. If you do, you have an issue with parallax. Some scopes are fixed and have no adjustment and some have an adjustment on the objective and those probably are more precise than the adjustments on the side.

The crosshairs need to be clear and crisp and the target should be clear at the range you are shooting and both MUST be in the same plane to minimize parallax.

I have never seen a system that was perfect but some do come pretty close.

The proper cheek weld is important to get your eye in the same relative position shot after shot. That will also reduce the effects of parallax.

The best parallax correction is when you can mount the rifle in a sled and look through the eyepiece without disturbing the rifle and view the target. If you can move your eye slightly off center both left and right and up and down, and see no apparent movement of the target relative to the crosshair, you have effectively removed the effect of parallax and the problem of target and crosshair not being in the same plane.

If you do see movement, it will affect your shot.

The other thing that is commonly misrepresented is eye dominance.

When you hold your eyes open and point your finger at a distant object, you are using your dominant eye for alignment.

If you close your left eye and the alignment is maintained, you are right eye dominant. If you close your right eye and alignment is maintained, you are left eye dominant.

Don't believe me? Take your empty handgun and align the sights with anything. Close your right eye. Target aligned? For most right handed people, the answer is no. For left eye dominant shooters, close your left eye.

This is not parallax.

This is also why right eye dominant shooters, when they use an adjustable diopter, affix it to their right lens on their shooting glasses.

I am not trying to be a wise guy, but I worked with alignment telescopes, bore sighters, jig transit squares and theodolytes for over forty years.

If you have ever looked at a precision pressure gage with a mirrored dial, you will experience parallax error if you view the dial from any point not perpendicular to the dial. This is because the dial pointer is not in the same plane as the dial...hence the error. The mirror dial is one way to correct for that error because it invites the calibration technician to adjust the view of the dial to minimize the view of the dial pointer on the plane of the dial.

I have experienced just about every optical malady that can crop up in an optical system, and my experience suggests parallax is right at the top of the list.

Sorry this is so long, but the error is there. It is significant and it is common and it can be corrected for, but you need to be aware of it.

Geetarman:D
 
"The best parallax correction ... If you can move your eye slightly off center both left and right and up and down, and see no apparent movement of the target relative to the crosshair, you have effectively removed the effect of parallax ...."

Amen, brother. I preach this to everyone I can. Properly adjusted, you can have terrible cheekweld, ( right left, up, down).

LOCATION OF EYEBALL DOES NOT MATTER if the scope is properly adjusted.
 
I never said it didn't exist but worrying about parallax IS insignificant for 99.9% of shooters and generally over discussed. We can talk about parallax till we are blue in the face but to the OP it's gonna mean nothing. All he and most other shooters need to know is that most centerfire scopes are factory adjusted to work best at a good variety of centerfire ranges, shotgun scopes at shotgun ranges and rimfire scopes at rimfire ranges. In other words pick the proper scope (in the OP's case a centerfire scope) and go shooting. Even if shooting at ranges that are different from the factory setting it's a fairly small issue when using a rifle and not enough to cause a miss on anything but very small targets.

Parallax is one of the many issues that have become a bigger issue to the masses since the introduction of the internet. There's whole generations of very good shooters that have gone thru life without ever hearing/seeing the word parallax or caring what it was. They bought a gun, they bought a scope, they killed things.

LK
 
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If you miss it's your fault not a scope/parallax issue.
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That is just not true.

The whole idea of shooting for groups is removing or minimizing the effects of variables.

If you are not interested in long range shooting, the issue is probably moot.

I see guys put round after round into one caliber holes, and they are able to do that because they pay attention to the variables that affect groups.

Some are easier to detect and control than others. Some have a greater effect than others.

A lot depends on exactly what you want to accomplish with your rifle shooting.

Parallax is generally easy to detect and control albeit widely overlooked as a source of error when shooting for groups.

Geetarman:D
 
Don't believe me? Take your empty handgun and align the sights with anything. Close your right eye. Target aligned? For most right handed people, the answer is no. For left eye dominant shooters, close your left eye.

This is not parallax.
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It is parallax in the general sense. Basically by changing your observation point (from your dominant eye to your non-dominant eye) you're creating an apparent change in position between the three objects (front & rear sight and target).

That's parallax in its most basic sense--the apparent change in position between objects at differing ranges caused by changing the observation point. The same effect can be seen when viewing needle gauges from the side instead of from directly in front of the gauge.

It's worth pointing out that parallax can't really cause problems with iron sights because the necessity of lining up three objects plus the observer will reveal any changes in position by the observer. That is, if the eye moves, the sights will no longer be aligned with each other and that will provide a clue that the entire system needs to be realigned.

With a scope, you aren't normally given any such clues. But you CAN be. When precision is critical, I adjust the eye-relief on my scopes so that I don't get the full field of view. In other words, I want to see a thin rim of black around the outside of the field of view. That lets me do a very quick check to see if my eye is centered properly by looking to see if that rim of black is even all the way around the edge. If it's not, I can adjust my eye position to correct the problem. The result is that I am always assured that my eye is centered in the scope.
 
Who in the heck is talkin shooting for groups or long range shooting. The OP? Not by a long shot. Me? No, I said insignificant for 99.9%. Yes, there is .1& of shooters that parallax might be an issue.

For hitting a critter, a man or a B27 target there is no need to worry about parallax or perfect objective adjustment WITH IN reason. Heck, even our military snipers use fixed objective scopes. You are taking what may be required in the target world (a very small part of the shooting community) and insinuating that most shooters should care and/or understand parallax which is simply untrue.

The simply answer to the OP's post is don't worry about it. Ya don't see pilots try to explain basic avionics to his passengers do you. Why? 2 reasons, they don't need to know and it may very well be over their head.

LK
 
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