Can someone please explain parallax?

[Atom Smasher]

So I recent picked up a scope for my .22 so I could do a little precision plinking, instead of using the irons. I've never really used a scope before, so I decided to read up on how to zero the scope and ran into terms (like parallax) that confused me. Can someone please explain scope mechanics or show me a resource that explains it simply?

Mods, please feel free to move this wherever you think it'd be appropriate, I just stuck it here because I figured this is where most people use magnified optics.

 

[Norrick]

Without explaining exactly how it works, parallax is responsible for the crosshair moving against the target background. It happens when you move your head slightly from side to side or top to bottom while looking through the scope. If you dont position your head exactly the same between shots you may be throwing flyers and not realize that it is your cheek weld.

The effect is more pronounced depending on what range the scope is calibrated to vs what range you are using it for.

Side focus and adjustable objectives are two different solutions to this problem.

You may notice that it is hard to focus on both the crosshair and the target at the same time (one moves into focus as the other moves out). Parallax adjustment also corrects this.

You can think of a regular scope a having a fixed parallax. It works the same but it had the parallax set to zero at a specific range from the factory and it cannot be adjusted.

 

[taliv]

when you're driving down the road at 70mph, you know how if you look at the speedometer from the passenger seat, it looks like about 65mph? that is parallax
(assuming you're not using a digital one... duh)

 

[WNTFW]

You have 2 objects. Both are at different distances.
1 is your target image in the scope
2 is your reticle image in the scope

If the parallax adjustment has the 2 images seperated It will only line up correctly if your eye is centered on the scope. Off center induces error

If the parallax adjustment has the 2 images on the same plane (no seperation) you can get away with eye being more off center.

The error depends on how off center your eye is & how far apart the 2 images are in the scope.

Place left hand at arms length palm facing you.
Place right hand half way in between & line up on hand perfectly with the other. Move head left then right. Hands appear misaligned. put puts hand together & they stay in apparent alignment.

 

[tyeo098]

Parallax is like when you look a something with your left eye, and then your right eye.
The image changes slightly.

Thats parallax.

(Its also how astronomers measure the distance to stars from Earth, with that and some clever geometry)

 

[kludge]

The cause of parallax in a rifle scope is due to the crosshairs being in a different focal plane than the object in view.

When the object in view is in the same focal plane as the crosshairs there is zero/minimum parallax.

Scopes with an adjustable objective (AO) allow you to compensate for objects at varying distances.

 

[kozak6]

Make a thumbs up sign and close an eye. Position your thumb on or over a "target" in the room. Move your head left and right.

Even though your thumb is in the same place, it doesn't appear to be lined up with your target anymore. That's parallax.

If you can hold your rifle the same way each time, it's less of a problem.