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 Can someone describe parallax to me and how it affects optics?
CrimsonTideShooter  [Team Member]
5/31/2011 11:48:58 PM
I've googled parallax but all the technical talk didn't really teach me anything.

How does parallax affect optics? I have an eotech than claims parallax free, and my vortex sparc claims it's parallax free past 50 yards.

What does it mean and how can l "see" what it means? Thanks guys.
TheTracker  [Team Member]
5/31/2011 11:54:50 PM

Originally Posted By CrimsonTideShooter:
I've googled parallax but all the technical talk didn't really teach me anything.

How does parallax affect optics? I have an eotech than claims parallax free, and my vortex sparc claims it's parallax free past 50 yards.

What does it mean and how can l "see" what it means? Thanks guys.

hold up your finger and close one eye.
Put it on a spot on your wall.

Then close that eye and open the other,

kind of like that.

When you put your cheek on the butt stock it should always be in the same spot.

Or maybe a better example is step on your bathroom scale. Then look at it from another angle.
The needle shows a different weight.
the_naked_prophet  [Member]
5/31/2011 11:58:41 PM
Originally Posted By TheTracker:

Originally Posted By CrimsonTideShooter:
I've googled parallax but all the technical talk didn't really teach me anything.

How does parallax affect optics? I have an eotech than claims parallax free, and my vortex sparc claims it's parallax free past 50 yards.

What does it mean and how can l "see" what it means? Thanks guys.

hold up your finger and close one eye.
Put it on a spot on your wall.

Then close that eye and open the other,

kind of like that.

When you put your cheek on the butt stock it should always be in the same spot.

Or maybe a better example is step on your bathroom scale. Then look at it from another angle.
The needle shows a different weight.


In other words, parallax is the difference between where the crosshairs are with your eyes in position A, vs. where the crosshairs are with your eyes in position B. It is why cheek weld is important, to be absolutely sure your eye is in the same place for each shot.
TheTracker  [Team Member]
6/1/2011 12:03:19 AM

Originally Posted By the_naked_prophet:
Originally Posted By TheTracker:

Originally Posted By CrimsonTideShooter:
I've googled parallax but all the technical talk didn't really teach me anything.

How does parallax affect optics? I have an eotech than claims parallax free, and my vortex sparc claims it's parallax free past 50 yards.

What does it mean and how can l "see" what it means? Thanks guys.

hold up your finger and close one eye.
Put it on a spot on your wall.

Then close that eye and open the other,

kind of like that.

When you put your cheek on the butt stock it should always be in the same spot.

Or maybe a better example is step on your bathroom scale. Then look at it from another angle.
The needle shows a different weight.


In other words, parallax is the difference between where the crosshairs are with your eyes in position A, vs. where the crosshairs are with your eyes in position B. It is why cheek weld is important, to be absolutely sure your eye is in the same place for each shot.


Yes
TrojanMan  [Team Member]
6/1/2011 12:04:27 AM
Originally Posted By the_naked_prophet:
Originally Posted By TheTracker:

Originally Posted By CrimsonTideShooter:
I've googled parallax but all the technical talk didn't really teach me anything.

How does parallax affect optics? I have an eotech than claims parallax free, and my vortex sparc claims it's parallax free past 50 yards.

What does it mean and how can l "see" what it means? Thanks guys.

hold up your finger and close one eye.
Put it on a spot on your wall.

Then close that eye and open the other,

kind of like that.

When you put your cheek on the butt stock it should always be in the same spot.

Or maybe a better example is step on your bathroom scale. Then look at it from another angle.
The needle shows a different weight.


In other words, parallax is the difference between where the crosshairs are with your eyes in position A, vs. where the crosshairs are with your eyes in position B. It is why cheek weld is important, to be absolutely sure your eye is in the same place for each shot.


And to eliminate parallax, you ensure that the reticle is on the exact same focal plane (focus distance) as the target. That way, instead of looking at two different objects, each a certain (potentially unknown) distance from each other, you're looking at a "2D" object like a picture on a flat piece of paper.

And just like the bathroom scale, the farther the two images are "apart," the greater the error. So for an inexpensive scope with fixed parallax that's factory regulated at 100 yards, the farther you get away from 100 yards, the worse the parallax error gets.

In a scope that doesn't have adjustable focus, you can minimize parallax by trying to make sure you're looking through the direct center of the tube. It's easier to do with scopes with extended eye relief where you just make sure to center the crosshairs in what you can see of the scope's body.
CrimsonTideShooter  [Team Member]
6/1/2011 12:06:55 AM
That makes very much sense guys. Thanks!


So with a sight that is "parallax free" cheek weld is less important?
TrojanMan  [Team Member]
6/1/2011 12:13:00 AM
Originally Posted By CrimsonTideShooter:
That makes very much sense guys. Thanks!


So with a sight that is "parallax free" cheek weld is less important?


It's important from a mechanics and fundamentals of shooting standpoint. It's not important in eliminating parallax error.
TheTracker  [Team Member]
6/1/2011 12:13:51 AM

Originally Posted By CrimsonTideShooter:
That makes very much sense guys. Thanks!


So with a sight that is "parallax free" cheek weld is less important?


Cheek weld is always important but with red dots it's much more forgiving.
Poodleshooter  [Member]
6/1/2011 12:15:27 AM
Google "maximum parallax error" or check out the wikipedia entry on parallax. You can calculate it for most scopes if you have their objective diameter and their parallax correction setting and the yardage you're shooting at. That helps you establish whether it's a worry or not.
Basically, if you move your head on the stock, and the optic is not parallax corrected for that exact distance, your crosshairs/dot will appear to move off of the target to some degree (the maximum of which is the maximum parallax error). Your shot will also move off of the point of aim.
Two ways to fix it:
-Always have your head in the exact same place
-Correct the parallax to the range.
The closer your parallax correction is to the actual range of the target, the less head movement will matter. That's why target scopes have either side focus parallax correction, or adjustable objectives. A properly parallax adjusted scope will let you move your head all over the place, while the reticle (and your point of impact) won't shift position versus the target.
BamaInArk  [Team Member]
6/1/2011 12:29:02 AM
As I understand it parallax is not an issue using nonmagnified optics like Redots or Holographic sights. The higher the magnification the higher the parallax error. If you want to see how it works(effects) try using an optical boresighter like the Bushnell. Twist your scope out to the higher or highest power setting and while looking at the pattern in the borescope move your head slightly from your cheekweld. If your scope is of lessor quality or not adjusted if it has a parallax adjustment you'll notice the crosshairs of the scope moving around on the target pattern in the borescope.

If you want a good technical description of parallax have a look at the posts on this older forum. Scroll down to the post from "Catshooter"...post #4.

LongRangeShooter