Calguns.net  

Home My iTrader Join the NRA Donate to CGSSA Sponsors CGN Google Search
CA Semiauto Ban(AW)ID Flowchart CA Handgun Ban ID Flowchart CA Shotgun Ban ID Flowchart
Go Back   Calguns.net > FIREARMS DISCUSSIONS > Optics, Mounts, Rails and Sights
Register FAQ Members List Calendar Mark Forums Read

Optics, Mounts, Rails and Sights If it aims your firearm, post about it here.

Reply
 
Thread Tools Display Modes
  #1  
Old 09-18-2009, 3:54 PM
67Roadster's Avatar
67Roadster 67Roadster is offline
Senior Member
 
Join Date: May 2006
Location: OC
Posts: 586
iTrader: 1 / 100%
Default Explain Parallax Free

Can someone explain Parallax Free?

I purchased this red dot sight (I'm cheap) and it says it is parallax free. If my understanding is correct, if you move your head the red dot stays in the same place. This doesn't happen on this red dot sight.

http://primaryarms.com/product.sc?pr...8&categoryId=5

Thanks.
Reply With Quote
  #2  
Old 09-18-2009, 3:57 PM
POLICESTATE's Avatar
POLICESTATE POLICESTATE is offline
I need a LIFE!!
 
Join Date: Apr 2009
Location: Sunnyvale, PRK
Posts: 17,839
iTrader: 25 / 100%
Default

Not exactly, here this will explain it:
__________________
If you want a picture of the future, imagine a boot stamping on a human face forever.


Government Official Lies
. F r e e d o m . D i e s .
Reply With Quote
  #3  
Old 09-18-2009, 10:11 PM
CRTguns's Avatar
CRTguns CRTguns is offline
Veteran Member
 
Join Date: Mar 2006
Location: St George, UT
Posts: 2,605
iTrader: 7 / 100%
Default

no magnifying, lensatic optic is truly parallax free. The greater the power, the greater the parallax.

Some non magnifying (red dots) are and some are not parallax free.
Reply With Quote
  #4  
Old 09-18-2009, 10:44 PM
rabagley's Avatar
rabagley rabagley is offline
Calguns Addict
 
Join Date: Apr 2008
Location: Near Seattle, WA
Posts: 7,188
iTrader: 21 / 100%
Default

There's no way to completely eliminate parallax (a difference in point of aim and point of impact caused when the eye is out of alignment with the sight and target).

Basically, if you bolt your rifle down and look through the scope straight on, you'll see the aiming point and the downrange target. If you move your eye to the left or right, you may see the aiming point over a different location on the target. That movement is parallax.

Hologram sights and most quality red-dot sights move the aiming point around in the field of view to compensate for parallax. Your red dot sight should change the location of the dot in the sight as you move your head behind the sight. If not, it's a REALLY cheap one, and you should probably return it unless you're putting it on an airsoft gun.

What these sights mostly correct for is the angular parallax (what's shown in the youtube video). However, none of these sights can perfectly compensate for combined angular and linear parallax at all ranges. If an EOTech window is 1.5" wide and the angular parallax is 100% perfectly eliminated, then moving your head to the left by .75" will move the reticle by .75" and move the point of aim by .75". That's full uncompensated linear parallax. They could under or over-correct the angular parallax so that the angular parallax perfectly overcame the linear parallax at a particular range, but they would be somewhat off at all other ranges (and potentially much farther off at long distances). I honestly don't know what their decision was. Probably it's perfect somewhere in the middle of the expected shooting distance (100-150 yards/meters).

For magnified rifle scopes that don't have the ability to project the reticle into the field of view, there is sometimes a parallax knob or adjustable objective that acts a lot like a focus knob (because that's part of how it works). The parallax adjustment puts the target and the crosshairs both in the same focus (you still have to adjust your eyepiece focus to let you see both clearly). What "putting the target and crosshairs in the same focus" does is makes sure that side-to-side movement of your eye causes a matching shift in your perception of both the crosshairs and the target, eliminating parallax.

Again, the combination of angular and linear parallax is minimized only for that one range. You'll have to change the parallax adjustment to the range you're shooting to keep it minimized. This makes sense for bench shooting, not so much for tactical shooting. If there is no parallax adjustment on a magnified optic, then the parallax is set to be a minimum at a known range, somewhere in the middle of the expected shooting distance (100 yards is fairly common). Really important: if you're going to mess with this setting, don't rely on your perception of "in focus" to do it. Your eye will compensate for poor focus if it's close and that ability to compensate will mean an incorrect setting. You need to fix the rifle in place, point it at a target of known range, then adjust the parallax setting until you can move your eye all around behind the eyepiece and the reticle/target image doesn't move. Mark the point on the knob, change to a target of a different range, wash, rinse repeat.

Something you can do to minimize the impact of parallax on your shooting is to keep your eye back from the scope so that you see a faint dark ring around the image. What you're doing there is exceeding the eye relief of the scope, so some of the image is being lost and some of the resolving power of the scope is being wasted. But what you're gaining is a visual indicator of how well-centered your eye is along the bore of the scope. If you're perfectly centered, the fuzzy dark ring around the outside will be even. If you're off center, there will be more black on one side than the other.
__________________
"Ecuador offers the United States $23 million a year in economic aid, an amount similar to what we were receiving under the tariff benefits, with the purpose of providing human rights training that will contribute to avoid violations of people's privacy, that degrade humanity," --Fernando Alvarado

Last edited by rabagley; 09-18-2009 at 11:08 PM.. Reason: added angular/linear parallax discussion
Reply With Quote
  #5  
Old 09-18-2009, 10:58 PM
L4D's Avatar
L4D L4D is offline
Veteran Member
 
Join Date: Sep 2009
Location: San Diego
Posts: 2,518
iTrader: 73 / 100%
Default

Quote:
Originally Posted by POLICESTATE View Post
Not exactly, here this will explain it:
wtf? that looks like magic? so how does the red dot stay on target if the scope moved like the way it did?
i understand it, but they need a better representation. lol
Reply With Quote
  #6  
Old 09-18-2009, 11:10 PM
rabagley's Avatar
rabagley rabagley is offline
Calguns Addict
 
Join Date: Apr 2008
Location: Near Seattle, WA
Posts: 7,188
iTrader: 21 / 100%
Default

The red dot isn't etched into the glass. An image of the dot is reflected into the sight so that if you're looking at the sight from a different spot, you see the red dot in a different spot.
__________________
"Ecuador offers the United States $23 million a year in economic aid, an amount similar to what we were receiving under the tariff benefits, with the purpose of providing human rights training that will contribute to avoid violations of people's privacy, that degrade humanity," --Fernando Alvarado
Reply With Quote
  #7  
Old 09-20-2009, 4:34 PM
maxicon's Avatar
maxicon maxicon is offline
Veteran Member
 
Join Date: Oct 2005
Location: San Jose
Posts: 4,598
iTrader: 23 / 100%
Default

Just to add a little more, most people don't really need to worry about parallax, especially with a red dot.

If you're doing precision shooting and counting the holes in the X ring, yeah, it can make a difference. If you're shooting inexpensive milspec ammo from a typical AR, the ammo's got a lot more variability than any scope you're likely to use.
__________________

NRA Life Member
Reply With Quote
  #8  
Old 09-23-2009, 12:16 PM
GrizzlyGuy's Avatar
GrizzlyGuy GrizzlyGuy is offline
Gun Runner to The Stars
CGN Contributor - Lifetime
 
Join Date: May 2009
Location: Northern Sierras
Posts: 5,469
iTrader: 0 / 0%
Default

See here, a great article on the subject:

http://www.brianenos.com/forums/inde...howtopic=31512
Reply With Quote
  #9  
Old 09-23-2009, 12:20 PM
POLICESTATE's Avatar
POLICESTATE POLICESTATE is offline
I need a LIFE!!
 
Join Date: Apr 2009
Location: Sunnyvale, PRK
Posts: 17,839
iTrader: 25 / 100%
Default

Quote:
Originally Posted by L4D View Post
wtf? that looks like magic? so how does the red dot stay on target if the scope moved like the way it did?
i understand it, but they need a better representation. lol
Yeah the representation does not account for the fact that it's your head that is moving out of alignment while the rifle is staying on target
__________________
If you want a picture of the future, imagine a boot stamping on a human face forever.


Government Official Lies
. F r e e d o m . D i e s .
Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump



All times are GMT -8. The time now is 1:42 AM.




Powered by vBulletin® Version 3.8.9
Copyright ©2000 - 2016, vBulletin Solutions, Inc.
Proudly hosted by GeoVario the Premier 2A host.
Calguns.net, the 'Calguns' name and all associated variants and logos are ® Trademark and © Copyright 2002-2016, Calguns.net an Incorporated Company All Rights Reserved.