Author Topic: Will Parallax causes greater problems at short distances?  (Read 314 times)

d_boom

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Will Parallax causes greater problems at short distances?
« on: November 21, 2018, 11:10:30 AM »
At what distances does parallax in a scope cause the most difficulty if it is not adjusted out?  I think parallax
causes more difficulty for airguns as the distance airguns are shot are usually short compared to distances
cartridge guns are shot.  Growing up shooting .22's mostly with open sights, but sometimes shooting .22's
equipped with a scope I had not heard about parallax let along seeing a scope adjustable for parallax.  Best I
remember the scopes we did use, cheap of course, did not cause us to miss what we shot at, but we were not
serious target shooters either. 


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rsterne

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Re: Will Parallax causes greater problems at short distances?
« Reply #1 on: November 21, 2018, 12:09:10 PM »
Parallax error occurs when the image formed by the objective lense is not in the same place as the reticle.... A scope that has parallax adjustment either moves the objective lense back and forth (AO) or it moves the reticle back and forth (SF) so that the image of your target is formed in the same plane as the reticle.... Once that is done, it doesn't matter whether you view the combined reticle and image from straight on, or an angle, they don't move, relative to each other....

When your target is at infinity, the image is formed some distance behind the objective lense, called the "focal length".... When the target is closer to the lense, the image forms slightly further back.... The closer the target to the lense, the greater that offset, compared to the focal length.... That is why both AO and SF adjustments require a greater change for close targets than for distant ones.... If you set the scope for infinity, and then look at a target that is only 10 yards away, the image formed inside the scope will be behind the reticle.... If you have the rifle in a vise and move your head side to side, the reticle will appear to move, relative to the target.... This apparent movement of the reticle, relative to the target, is what we call "parallax error".... Likewise, if you have the scope adjusted for a target that is 10 yards away (by increasing the distance from the lense to the reticle), and then look at a target at infinity, the image will form in front of the reticle.... Moving your head side to side will also cause the reticle to appear to move on the target, but in the opposite direction....

There is a focus adjustment on the eyepiece (called the ocular adjustment), which you are supposed to adjust so that the reticle is in sharp focus for YOUR eye.... This is best done by setting the AO or SF to infinity, and looking PAST the reticle to a cloudy sky, ie a bland, low contrast background but with some features you can focus on.... You then adjust the focus ring on the eyepiece until the reticle is sharp, WITHOUT LOOKING AT IT, but still looking past it at the clouds.... Once this is done, lock down the focus ring and never touch it again.... Regardless of the distance to your target, the RETICLE will now always be in sharp focus.... 

If the AO or SF on your scope is set to the proper distance to the target, since the image of that target is being formed exactly at the reticle location, the target will also be in sharp focus, and you will have no parallax error.... If the AO or SF is set too close or too far away, the image may not be as sharp, and you will be introducing some parallax error as well.... This is most noticeable at high magnifications, which have a smaller "depth of field", which means the distances between which the image still appears sharp.... The depth of field gets smaller, the closer you are to the target.... That is why you have to move the AO or SF more at short ranges.... You may have to move the AO ring 1/4 turn between 10 yards and 50 yards, but hardly at all between 100 yards and 200 yards.... A glance at how far apart the ranges are on your AO or SF ring shows that clearly....

Therefore, to answer your question, parallax error occurs when you don't have your scope adjusted for the range to your target.... It is caused by the DIFFERENCE in that distance, and the parallax error between 10 and 20 yards could easily be the same as between 100 yards and infinity.... In practical terms, that means parallax error is more common, and larger, at close ranges....

Bob
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Nicesurprice

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Re: Will Parallax causes greater problems at short distances?
« Reply #2 on: November 21, 2018, 12:36:49 PM »
Knowing that.
Shooting at moving targets.
Or when not allowed to adjust youre scope ( HFT ).
A small eye relive is handy.

When youre not in perfect posision behind youre scope.
You wont have a view.
So small eye relive forces you in a good posision.
So you will not have ( or lhave ess)that error when the scope is not perfect set.

Grts
« Last Edit: November 21, 2018, 12:38:44 PM by Nicesurprice »
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Alan

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Re: Will Parallax causes greater problems at short distances?
« Reply #3 on: November 21, 2018, 01:01:35 PM »
Yes, and using lower power helps to, especially on moving targets.

I have always been of the opinion, that most scope users over scope their rifles. That is to say, much more magnification than they need for the task at hand. It is understandable (perhaps) for Field Target contesters to use high magnification. But why would you use a 10X to 30X scope on a hunting airgun where the max distance is under 100 yards in most cases? I hunt pigeons almost every day, year around. I have my scope (1.5X to 6X) set at just over 4X where the vertical graduations are exactly 4 inches apart at one hundred yards. I keep the side focus at 50 yards, and don't adjust it unless the distance is over 100 yards. What little parallax there is, is still within the kill zone of a pigeon.
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d_boom

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Re: Will Parallax causes greater problems at short distances?
« Reply #4 on: November 24, 2018, 11:17:27 AM »
Thanks rsterne for the great explanation of parallax.  You confirmed my experience of more parallax problems
experienced with shooting airguns usually shot at close distances, 10 meters, vs shooting cartridge gun at 50
to 200 yards.  On trips out to the gun range, I often shoot airguns 50 to 100 yards.
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caniborrowsomeammo

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Re: Will Parallax causes greater problems at short distances?
« Reply #5 on: November 25, 2018, 09:44:36 AM »

Or when not allowed to adjust youre scope ( HFT ).


Grts

You cannot adjust your parallax when in an HFT match???

   In Hunter class AAFTA says :
 B. No turret adjustment allowed during the match. (No clicking.)
 C. Optical sights with parallax adjustment may be adjusted so that
the target is in focus. Range (yardage) markings may be used.

http://www.aafta.org/Assets/handbook/2015/AAFTA_Handbook_2015.pdf

Or do European rules differ than American rules?
Buncha BB guns that I don't get to shoot as much as I like. Building duck boats now that I'm "retired".

Nicesurprice

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Re: Will Parallax causes greater problems at short distances?
« Reply #6 on: November 25, 2018, 10:03:29 AM »

Or when not allowed to adjust youre scope ( HFT ).


Grts

You cannot adjust your parallax when in an HFT match???

   In Hunter class AAFTA says :
 B. No turret adjustment allowed during the match. (No clicking.)
 C. Optical sights with parallax adjustment may be adjusted so that
the target is in focus. Range (yardage) markings may be used.

http://www.aafta.org/Assets/handbook/2015/AAFTA_Handbook_2015.pdf

Or do European rules differ than American rules?

Vergroting, parallax, turrets, instelling verlicht draadkruis DIENEN VOOR AANVANG van de wedstrijd ingesteld te zijn en MOGEN TIJDENS DE WEDSTRIJD NIET GEWIJZIGDWORDEN!Nietnakomenvandezeregels betekentdiskwalificatie!Op descorekaartdientvooraanvangvandewedstrijd devergrotingenparallaxinstelling ingevuld te worden.

Think they are different.
For HFT its not allowed to adjust anny parameter on youre scope.

Second word Parralax
Last line in capital letters “mogen niet verteld worden”.  Free translated can not be adjusted.

So think different rules.
Learning everly day we do. 😜
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Alan

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Re: Will Parallax causes greater problems at short distances?
« Reply #7 on: November 25, 2018, 11:48:33 AM »
All of this makes me wonder! What if you were allowed to use any means and/or adjustments and/or instruments, to make sure your pellets hit where you aimed... How precisely could groups be shot?

And just for the record... The best (screamer) group, ever shot from a firearm (6 mm PPC), measured .007 inches, center to center, at 100 yards.
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caniborrowsomeammo

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Re: Will Parallax causes greater problems at short distances?
« Reply #8 on: November 25, 2018, 12:22:55 PM »
So much for standardization among HFT rules around the world, Dutch rules are mighty strict, even compared to British rules on sighting which states per the SWEFTA:

All parallax and magnification adjustments for each target must be made unsighted, ie, without looking through the scope and before raising the scope to the eye. Once the rifle is mounted, no changes may be made. If the safety whistle blows after mounting and before the shot is taken, the scope cannot be altered in the period before the “All Clear!”

Which at least lets you "guesstimate" parallax setting.

With the AAFTA rules, my Sightron 10-50 really gets me accurate on ranging. I range on around 30x and shoot at 10 and 12x.

« Last Edit: November 25, 2018, 12:39:15 PM by caniborrowsomeammo »
Buncha BB guns that I don't get to shoot as much as I like. Building duck boats now that I'm "retired".

Nicesurprice

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Re: Will Parallax causes greater problems at short distances?
« Reply #9 on: November 25, 2018, 12:49:56 PM »
All of this makes me wonder! What if you were allowed to use any means and/or adjustments and/or instruments, to make sure your pellets hit where you aimed... How precisely could groups be shot?

And just for the record... The best (screamer) group, ever shot from a firearm (6 mm PPC), measured .007 inches, center to center, at 100 yards.

We have examples with 9 and 10 mm groups.
5 shots 100 meter

Today we did see official targets with over 10 shots in a 10 mm bullseye.
We use center measuring BTW. 
The bigbore cup stopt shooting groups because they simply can’t count the points.
So we shoot 30 1 shot targets.
They had situations only 3 shots where counted visualy.
So where did those other 2 shots go ??
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