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Importance of parallax adjustment?

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/10/2008 at 11:50
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At what magnification/distance does parallax adjustment become critical? I know that with a repeatable cheek weld it becomes less of an issue, but if I decide to be wierd and try to shoot out to 600 or 1000 yards with a non parallax adjustable lower magnification scope, how much of a problem will it be?
 
Is the problem minimised with lower powers (4x, or 6x), or does it only become apparent when going over 10x? I can still find "tactical" scopes (Khales and IOR) that are at 10x with no parallax adjustment, are they just behind the times, or is it that small of an issue within a given magnification/distance envalope?
 
I'm asking because I like lower power optics and am considering either a fixed 6x, 2.5-8, or 3.5-10 scope for my rifle. The first two wouldn't have parallax adjustment, the last could be had with or without, without costing less (obviousely).
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/10/2008 at 12:00
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Parallax can be an issue at longer distances, due to the nature of the projectile travelling along a given path. the greater the distance the further it will be off. Naturally the higher the magnification the smaller the aiming point, however this is only to a point. Most scopes that are parallax free are out to 100 yards, anything closer your fine, anything further and you will see some wandering around the POI.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/10/2008 at 12:46
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Back on May 31 Chris posted a very erudite explanation of parallax.  Do a Search on parallax and you will find it and a number of others.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/10/2008 at 13:08
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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/10/2008 at 13:26
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Thank you, Dogger.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/10/2008 at 13:37
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 Yea thanks  dogger ... saved and put that in my lil notebook of facts . Some of the guys here actually think I am close to an expert with my info I've collected from this forum .... they don't know where I saved and printed all the material from ... joke's on them .... huh ? Nawww .... I tell them ! Ya learn from the best ... and they're here !
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Adjustable parallax is preferable. However the IOR 6x42 Tactical even without adjustable parallax should be a formidable scope out to 600 or so yds. If you are going to pay more money for a  better scope than that I would expect it to have adjustable parallax. One big advantage of a fixed power is that you can use the marks on the reticle for know hold over as the power is always the same the point of impact drop due to trajectory is always the same.  What scope did you have in mind?
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/10/2008 at 23:40
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Thanks, guys.
 
That explains what I had heard about magnification having an effect on parallax.
 
 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/10/2008 at 23:45
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I was looking at the leupold FXIII 6x42. I see that they have a target version that comes with an adjustable objective, but it isn't available with M1 turrets. While I know target turrets and M1's will do the same thing I'd really rather not have to mess with turret caps.
 
Also, neither is available with the Tactical Milling Reticle Really%20Sad
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/11/2008 at 02:29
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The custom shop should be able to put M1's on that--they'll do it on 1" tubes now--but it will add a little to the price, of course.

To your question, I really wouldn't worry about AO on a 6X and it usually won't be much of an issue on your typical 9X-10X though you don't want to completely ignore it.  One of my small gripes with the IOR 2.5-10 is that it seems the parallax is set dead on for 100 m.  That's great for 100 yd groups but there is more parallax than I'd like at longer ranges.  It's not a deal breaker if you're aware of it, I've done fairly well with it out to 1000 yds, but it sort of bugs me.   I wish they would have set it for 200 or 250; 100 yd groups might open up a bit but it would be better for my uses. 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/11/2008 at 09:52
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The Leupold custom shop lists the 6x42 AO as not available for any custom knobs, I beleive b/c it uses 1/8 moa clicks instead of 1/4 moa clicks in the target turrets.

And as far as a parallax set farther out than 100 yards, the custom shop can set your parallax to whatever distance you specify for (I beleive) $15.00
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/11/2008 at 13:03
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Ah, my mistake.  1/8 clicks are a PITA anyway.  If you got a regular 6X42, 3.5-10, etc you could have the custom shop put M1's on it and set the parallax at the same time; you'd be all set.     Wink    Well, other than the fact it'd be a Leupold....      Bandito
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/11/2008 at 13:45
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Originally posted by Jon A Jon A wrote:

The custom shop should be able to put M1's on that--they'll do it on 1" tubes now--but it will add a little to the price, of course.

To your question, I really wouldn't worry about AO on a 6X and it usually won't be much of an issue on your typical 9X-10X though you don't want to completely ignore it.  One of my small gripes with the IOR 2.5-10 is that it seems the parallax is set dead on for 100 m.  That's great for 100 yd groups but there is more parallax than I'd like at longer ranges.  It's not a deal breaker if you're aware of it, I've done fairly well with it out to 1000 yds, but it sort of bugs me.   I wish they would have set it for 200 or 250; 100 yd groups might open up a bit but it would be better for my uses. 


I agree, out here on West Coast, where we hunt, we have longer shots and having parallax set for 200 yards would be nice.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/11/2008 at 14:01
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As to picking a parallax distance for a fixed parallax scope, I found this:
 
Now can we calculate?  Oh, goodie!  On a short scope, the objective's focal length must be around 0.1 m considering that there is an erector lens in that tube also.  The formula for the distances from a lens of the object and the image of that lens is:
                            O^-1 + I^-1 = F^-1
where:
                  O = distance from object to lens
                  I = distance from image to lens
                  F = focal length of lens

What I'd like to know is how far we'd have to bring the objective lens in if we shift the parallax correction from 50 m to 100 m.  Moving the objective lens relative to the scope body makes no essential change in the value of the variable, O.  So how far is the image from the lens when the target is at 50 m?   100 m?   150 m?

        I(50) = [(F^-1)- (O^-1)]^-1 = [(.1^-1)-(50^-1)]^-1 = .1002 m
        I(100) = [(.1^-1)-(100^-1)]^-1 = .1001 m
        I(150) = [(.1^-1)-(150^-1)]^-1 = .10007 m

Sooooo, if I can find the focal length of the scope I want, and I can have the parallax adjusted to any distance I want at the factory, I can figure out a distance that would be in the middle of the range I'd like to shoot. And by using this formula I could figure out what my parallax error would be at any other given range other than the one it is pre-dialed in for, I think.


Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/11/2008 at 14:08
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Sounds like a plan.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/11/2008 at 14:55
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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/11/2008 at 14:56
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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/11/2008 at 19:25
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Originally posted by Jon A Jon A wrote:

Ah, my mistake.  1/8 clicks are a PITA anyway.  If you got a regular 6X42, 3.5-10, etc you could have the custom shop put M1's on it and set the parallax at the same time; you'd be all set.     Wink    Well, other than the fact it'd be a Leupold....      Bandito


I agree with the 1/8 statement.
On the other hand I do have a now discontinued 6x42 Tactical Leupold. It has adjustment down to 50 yards and up to infinity, which is far more than adequate for my purposes. It is one of my best scopes including several Kahles C types.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/11/2008 at 20:01
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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/13/2008 at 18:12
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You know, the more I talk to my shooting budies that do long range stuff the more that looks like the best idea. Buy the right thing the first time, right?
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/13/2008 at 20:28
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Parallax and low power ( under 10x) scopes.
At first glance it really seems unimportant at any range with say a 4 or 6x unit.
One of the things that might be considered is that with these scopes it's not always possible to define  the aiming point on the target well enough to know if you're experienceig a parallax error.  Sight alignment looks good, trigger break is fine, impact is reasonably close to our aim point at 100-300 yards.
If we boost the magnification to just 10x, a more refined aiming point can be defined, and the effects of parallax can be experienced.  On a 10x scope with the reticle properly focused,, rifle rested solidly,  the error in parallax between not adjusted and properly adjusted to range and light can be 50% of the size of your group.  This is just at a mere 100 yards.
 
Having had the opportunity to shoot behind an MST 100 scope, parallaxed for 300 yards, the effects of a non-adjustable scope at shorter and longer  distance can be eye opening.  Everything becomes critical, NPA, head postition, grip, trigger press and follow through.
 
Having said all that, if it's a hunting scope you may have minimal time to line up a shot that only has to be placed on a 2 moa spot, so parallax may not have any real meaning in that context.
If we have longer distance and smaller, more critical targets, I'd say get the adjustable unit and save at least one point of frustration.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/13/2008 at 21:37
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Very good points.  "Conventional wisdom" has always said you don't need to worry about it at 10X or under.  But as mentioned before, that isn't always the case.  It's one of the reasons my 2.5-10 IOR has been replaced with a much crappier scope and will likely be sold.  I love it to death, but that's one feature I think it really needs for my uses.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/14/2008 at 06:46
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Parallax can be defined as the apparent shift of the aiming point on the target caused by moving your head(eye). The greater the magnification the easier it becomes to see this apparent shift. Generally at 10X and above this apparent shift becomes very noticeable.

When it comes to distance, the apparent shift becomes noticeable at SHORTER distances, not longere distances. Light moves in a staight line. Therefore the further the object (target) is away from you the more you will naturally find the center parralax free alignment on your telescope.
This is why a hunting scope is parallax free at 100 yds. It gives you a shootable situation at shorter distances and at longer distances it becomes less of a problem.
Airgun target shooters who shoot at 10 and 25 yds all have parralax adjustable scopes, because it is at this short distance that it plays the biggest role in accuracy.
So in my opinion, if you are going to shoot out to 300 yds + an adjustable parallax is not a big deal. I would also not set my parralax in at say 200yds. Your 100yds and less shots will become a nightmare.


Edited by 8shots - July/14/2008 at 06:47
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/14/2008 at 08:26
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Great info guys!! 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/14/2008 at 09:06
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 Don't move your head .... LOL
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