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Parallax vs Focus

 
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  #43  
Old 05-07-2006, 04:01 PM
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Re: Parallax vs Focus

Maybe I am way off base but I think the confusion may be with how different scope models work.

Burris scopes (the ones I have seen) have the abillity to Focus just the reticle by turning the eyepiece cushion. This adjustment is seperate from the magnafication adjustment and Paralax(objective) adjustment.

I have not seen a Leupold with this feature but I'm sure they make them.

Scopes have a Paralax range(for lack of a better term). This is the range that the paralax is pre adjusted for. On pistol scopes this is commonly about 50 yards. Rifle scopes I think it is around 100 yards. Pistol scopes tend to have alot of Paralax (jumpy crosshair) at short ranges encounterd while testing scopes in stores at gun counters. I think this has to do with distance between lenses but not sure. At any rate this parallax makes little difference to short range pistol work.

Rifle scopes often have an adjustable objective so that the operator can adjust the paralax range for long range shooting where paralax can have an effect.
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  #44  
Old 05-07-2006, 05:50 PM
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Re: Parallax vs Focus

Chesapeake, all rifle scopes have an eyepiece at the back end to focus the reticule so folks can see it clear and sharp. That's the only reason the eyepiece is adjustable; we each have different eyeball focal lengths and the eyepiece lens compensates for that by being adjustable.

Parallax usually causes more problems at short range than long range. The higher the magnification and closer the range, the more problems parallax can cause. This is why pistol scopes have more parallax problems than rifle scopes.
Learn how to center your eye in the pistol scopes optical axis and there will be no parallax.

Note that as long as the aiming eye is on the scope's optical axis, there will be no parallax problem regardless of what range the objective lens is focused at. Which is why there really isn't any such thing as "parallax adjustment" on a scope. Scope makers have confused more people by claiming such a thing, but they don't care.

It's not "parallax range" but focused range. The adjustable objective lens is marked from infinity back to some close range in yards, meters, feet, whatever unit the maker chooses. The only thing the front (objective) lens group does when it moves is change the range the target will be sharply focused on the reticule. It has nothing to do with parallax except when the aiming eye ain't on the scopes optical axis.

If one sees the reticule move relative to the target, this is a parallax condition that happens only when the scope's focused at a range different than the target AND the aiming eye's off the optical axis. It has nothing to do with the lens spacing.
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  #45  
Old 05-08-2006, 08:26 PM
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Re: Parallax vs Focus

Bart, I cant help but think you are both over complicating and over simplifying terms and descriptions as you see fit to try an prove what ever it is you are trying to prove.

I also dont think ALL rifle scopes have adjustable eyepieces, atleast not user adjustable. I have a few that do not.

I also dissagree on your comments about parallax and having nothing to do with distance between lenses on pistol scopes.

The idea that there is no parallax problem you just need to have your eye in perfect line with the plane of the scope is odd. The whole idea is that the optics be user friendly and allow a bit of variation on the part of the user.

I believe the short focal length of the lens assemblies in pistol scopes is what adds to thier being somewhat more critical to eye position than rifle scopes.
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  #46  
Old 05-09-2006, 12:01 PM
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Re: Parallax vs Focus

Rick, go someplace (your local city library?), find information on optical formulas, understand them, then put them to use designing individual lens group focal lengths and positioning for telescopic sights of different physical size and magnifications; zooms included. It's grade-school math for the most part. Then you will understand why I said what I did.

What scope make and model doesn't have an adjustable eyepiece? Just curious......
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  #47  
Old 05-10-2006, 09:17 AM
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Re: Parallax vs Focus

Bart,
In the intrest of not wasting any more of my time on this I will forfeit this one to you. I think it is safe to say that this thread has wandered out of the relm of usefull information. Thanks for your participation.
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  #48  
Old 06-06-2006, 09:58 PM
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Re: Parallax vs Focus

[ QUOTE ]


The idea that there is no parallax problem you just need to have your eye in perfect line with the plane of the scope is odd. The whole idea is that the optics be user friendly and allow a bit of variation on the part of the user.



[/ QUOTE ]

I have had a couple of scopes in the past with a lot of parallax and reload for some of my friends rifles that have a lot of parallax. There is an easy way to make sure that you are lined up directly in line. If the scope is on your gun, just move the scope forward in the rings until you start to get that black circle when the eye relief becomes too great. Center the circle around the edges and you have lined everything up and negated parallax. If you can't move the scope, then move your head back on the stock until you can get the black circle and center it.

Better to get a scope 10x or less and no parallax or buy a scope with an adjustable objective, but this helps you shoot smaller groups at the bench.
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  #49  
Old 08-12-2006, 10:16 AM
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Re: Any responses, please?

[ QUOTE ]
Regarding my previous post I was hoping for some response from Dave and Catshooter
Hey guys! I read your string of posts and found them quite informative as I am currently setting up my new Leo Vari-XIII 3.5-10x40 LR M3. I used Catshooters instructions for setting up the scope and ran into an issue when trying to zero the AO side knob. I focused in on an object at aprox 400M (the farthest I could conveniently find without obstruction) and played with the AO knob as Catshooter instructed. I started at infinity and worked my way back until I was parallax free. I was concerned that this point was at the middle dot on the adjustment knob so I went thru the process again starting back at infinity. The result was the same so I loosened the screws and reset the knob so infinity lined up with the hash mark. Now the knob bottoms out at the low magnification end around the second dot and consequently turns way past the infinity mark on the top end. I called Leupold to ask their feedback and the WOMAN who answered the tech line basically said that the knob is set at the factory and not meant to be adjusted. I obviously mentioned that there is adjustment screws on the knob which usually means they are there to enable adjustment but she stuck to her limited insight. I knew I was not getting anywhere so I came back here to ask the gurus for their guidance. Please advise. Thanks!

[/ QUOTE ]



I appologize for not getting back to answer this - I moved in 2003 and the move was a nightmare (took 8 months to move all the "stuff"), but the good part is now I have a poured concrete gunsafe that has 10' x 20' floor space with 10 foot high walls, and the walls are covered with pegboard (and covered with guns [img]/ubbthreads/images/graemlins/smile.gif[/img] ).

And since then I have been fighting a custody thing in court - so I haven't been on the web very much.

As to the lady at Leupold saying that they are set at the factory - BS. The people on the customer phones have a FAQ sheet in front of them with canned answers. They don't understand what or how scopes work. Since the "side focus" dials have no graduations, there is nothing they can set - it's an approxmation and you can do better. Just follow the instructions above. Set the dial at infinity (using an infinity subject). It doesn't have to be a real target - it can be a mountain ridge or whatever. When properly set, it will work fine - you can put a sticky lable arouind the knob and mark the closer ranges if you like, then, if you use a laser, you can set the range (start from infinity) correct your elevation, and shoot.

-

Bart B

[ QUOTE ]
Reticules in the first image plane also appear to move off center as elevation and windage adjustments are made. This happens 'cause the back of the erector tube is fixed and the front points to a different place in that first image. The only way to fix this is to anchor the erector tube's front end at the first image plane then move the adjustment turret back closer to the eyepiece. Which wouldn't be a bad idea 'cause the adjustments would be easier to reach.

[/ QUOTE ]

Not so... there are many first focal plane reticles still made and the reticle always stays in the center of the scope - what you are talking about was back in the '40s and '50's, the elevation/windage dials moved the reticle itself, and no optics were moved, so the reticle moved off center in the field, sometimes way off to one side or corner... but no one has made scopes like that in 50 years - now, in first focal plane scope, the optics are used to move the image, and the reticle ALWAYS stays centered.

-

CatShooter.

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