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Topic ClosedParallax-letting the genie out of the bottle again

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Direct Link To This Post Topic: Parallax-letting the genie out of the bottle again
    Posted: January/04/2010 at 02:34
A little while ago I posted a thread that had some definitive answers about the actual influence parallax has on GENERAL shooting accuracy. This article seemed to indicate that for most tactical and hunting purposes parallax error is not such a big deal. On the other hand if you are shooting benchrest and are looking for 1/8inch groupings, then parallax error does play a role.
I further suggested that good consistant cheek weld plays a bigger role then having a scope with zero parallax error.
 
This week-end I took a 25X side focus scope and put this theory to test.
This test was done at 100m.
The rifle was first zeroed, then the rifle was shot in random order. With the scope parallax eliminated no movement of the reticule was detected if I moved my head. With the parallax  poorly adjusted the reticule moved to allmost the edges of the circular target as I moved my head behind the scope. (It was bad, believe me.)
In each case proper attention was paid to consistent cheek weld.
Also, with the parallax dialed out, shots were fired with scant regard for cheek weld.
 
I post the target below.
Who would hazard a guess which settings were used for A, B, C and D????
Your choices are Zeroing, Zero parallax with good cheek weld, Zero parallax poor cheek weld, poor parallax with good cheek weld.
(And yes, I will try a similiar experiment at 300yds when I get the chance.)
 


Edited by 8shots - January/04/2010 at 02:44
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Direct Link To This Post Posted: January/04/2010 at 07:54
C&B poor cheek weld?
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Direct Link To This Post Posted: January/04/2010 at 08:09
You're not making this easy Wouter!
 
Zero - D
ZPGCW - A
ZPPCW - C
PPGCW - D
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Direct Link To This Post Posted: January/04/2010 at 08:59
Get Your Popcorn Ready
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Direct Link To This Post Posted: January/04/2010 at 09:24
Originally posted by mike650 mike650 wrote:

Get Your Popcorn Ready
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Direct Link To This Post Posted: January/04/2010 at 09:52
D:  Zeroing

A:  Zero Parallax, Good Cheek Weld
C:  Zero Parallax, Poor Cheek Weld
B:  Poor Parallax. Good Cheek Weld
 
Pass the popcorn, please...
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Direct Link To This Post Posted: January/04/2010 at 10:46
8shots, my PPGCW choice was supposed to be "B" - doubled on the D
 
p.s. you do Do intent on enlightening us right?
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Direct Link To This Post Posted: January/04/2010 at 11:27
d: zero par, good weld
a: zero par, poor weld
c:  par, good weld
b: zeroing
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Direct Link To This Post Posted: January/04/2010 at 14:33
Interesting.  You did a good job of keeping all the groups pretty decent.  But I'm more worried about the POI moving all over the place.
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Direct Link To This Post Posted: January/05/2010 at 01:29
Hats off to those who were brave enough to hazard a guess!!!!
 
To ease the pain.......
 
Target A was a cold barrel / fouler shooting. Prior to this excercise I had removed the scope for a minor gun repair job. So target A was the first shots after re-fitting the scope.
 
I then dialed one click right.
 
Target B is poor parallax, with a good cheek weld. This is in my opinion a decent/acceptable grouping.(0.64 of an inch or 15.38mm)
Target C is good parallax, but poor cheek weld and probably poor trigger work as a result of poor rifle holding.
Target D is good parallax and good cheek weld, again showing a decent/acceptable grouping. (0.599 of an inch or 14.36mm)
 
Due to the parallax being off on B, the focus was also poor. The black point on target B  (bottom right) became a better aiming point, accounting for the slightly low and right impact point.
 
JonA, the impact point shifting has been explained, but it is in my opinion a non issue, as the impact point can be shifted back to bull by dialing the turrets if a consistant grouping can be achieved.
 
The point is this, can a rifle group well enough for hunting purposes at 100yds with a scope with a bad/poor parallax setting?
I think it can. This parallax was bad, more then a "normal" scope without parallax adjustment. Mine was set for about a 300yds parallax free setting. Yet it allowed me to group under 1MOA.(With a rather blurry sight picture.)
 


Edited by 8shots - January/05/2010 at 04:48
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Direct Link To This Post Posted: January/05/2010 at 03:50
It was further suggested by someone (in a different thread), that errors are accumalative. In other words poor trigger control (say 1 inch)+ poor barrel (say 1 inch) will add to a two inch grouping. The same argument was used for parallax error.
 
My rifle seemed to group at less then 3/4 inch (See target D). The maximum parallax error for my scope (50mm lens with parallax fixed at 300 m) would be 33mm or 1.26 inches at 100 yds.
 
If the errors were accumalitive, as suggested, then target B should show a grouping of close to 2 inches. It does not.


Edited by 8shots - January/05/2010 at 03:54
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Direct Link To This Post Posted: January/05/2010 at 05:59
Originally posted by 8shots 8shots wrote:

JonA, the impact point shifting has been explained, but it is in my opinion a non issue, as the impact point can be shifted back to bull by dialing the turrets if a consistant grouping can be achieved.

Non issue?  It's the only issue.  It'll open your group if you can't hold it shot to shot, but if you can and can shoot small groups that still isn't good enough unless you can shoot group after group to the same POI.

Remember you're talking about hunting, where you may be in shirtsleeves or really bundled up, you may be wearing a thick wool cap or you may not, you may be in prone or you may be sitting, you may be shooting uphill you may be shooting downhill....  Counting on your ability to get the exact perfect weld as you can on the range because if you don't the crosshairs aren't where you think they are is setting yourself up for a poor shot in the field, IMHO.
Originally posted by 8shots 8shots wrote:

This week-end I took a 25X side focus scope and put this theory to test.
This test was done at 100m.

Unfortunately, putting the "theory to the test" would have meant:
Originally posted by Jon A Jon A wrote:

Try setting it at 100 next time and I think you'll find the 400 yd targets very difficult

Quite a different test.  Because: 
Quote The point is this, can a rifle group well enough for hunting purposes at 100yds with a scope with a bad/poor parallax setting?
I think it can. This parallax was bad, more then a "normal" scope without parallax adjustment. Mine was set for about a 300yds parallax free setting. Yet it allowed me to group under 1MOA.(With a rather blurry sight picture.)

No, that wasn't the point.  The point was:
Originally posted by Jon A Jon A wrote:

A scope with a lot of parallax at 600 yds simply isn't the best tool for shooting at 600 yds, regardless of what the shooter's "hold ability" is.

That was your original argument.   Proving it's good enough for "hunting purposes at 100 yds" is a completely different arguement.  Also
Originally posted by 8shots 8shots wrote:

It was further suggested by someone (in a different thread), that errors are accumalative. In other words poor trigger control (say 1 inch)+ poor barrel (say 1 inch) will add to a two inch grouping. The same argument was used for parallax error.
 
My rifle seemed to group at less then 3/4 inch (See target D). The maximum parallax error for my scope (50mm lens with parallax fixed at 300 m) would be 33mm or 1.26 inches at 100 yds.
 
If the errors were accumalitive, as suggested, then target B should show a grouping of close to 2 inches. It does not.

Nobody ever suggested the maximum possible parallax error would be added to your group size.  Even your original claim:
Originally posted by 8shots 8shots wrote:

Now if a half decent shooter halves that error with proper cheek weld,...

Was that you could cut it in half.  It was your contention that since nobody could shoot 1/2 MOA anyway, this would not increase group size at all that drew disagreement.  Do those 400 yd and 600 yd tests and get back to us on that one. 
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Direct Link To This Post Posted: January/05/2010 at 17:16
Thanks for sharing that Wouter!  I see and understand your intent!  And if I am ever in a hunting situation where my scopes parallax goes south I will know I can still attempt ethical shots and just by choice not attempt the longer shots pass ~300yds.  At least I would still be able to hunt with some level of confidence for larger game out to 250yd.
 
I also understand what JonA is saying.  I however instead of argueing just for the sake of argueing the splitting of hairs is more appropriate for the bench than the field.
 
Hope that last post didn't kill this thread.......HINT, HINT
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Direct Link To This Post Posted: January/06/2010 at 00:43

Budperm, at least you see what I am trying to show.

JonA, my first post in this thread says that I intend to do the longer distances test as soon as I can get to the long distance range.
 
I agree with you JonA that my test is not definitive and exhaustive, but as proved,  at 100yds and closer, with a CONSISTANT CHEEKWELD, parallax error can not to be blamed for missed shots. Nowhere in this thread did I talk about applying this information to any distance beyond 100m.
 
 
 
 
 
 


Edited by 8shots - January/06/2010 at 00:50
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Direct Link To This Post Posted: January/06/2010 at 06:48
Wouter I am sure JonA understands your intent, he is no dummy.  He just likes to argue for the sake of argueing sometimes.  I found this thread interesting and still what to see your results from the longer targets.  If your mechanics of aim are good and repeatable then I would think that the lack of focus the usually goes with bad parallax will cause an opening up of groups simply do to the fuzzy enlarged site picture and loss of a crisp small bullseye.
 
Thanks again for sharing Wouter, interest stuff!
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Direct Link To This Post Posted: January/06/2010 at 07:12
Thanks Wouter, interesting exercise and observations!
 
.....Bud where is your guess work??
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Direct Link To This Post Posted: January/06/2010 at 07:22
That wasn't brown enough for your Craig?
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Direct Link To This Post Posted: January/06/2010 at 07:39
You have me convinced bud but Wouter is a hard sell!
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Direct Link To This Post Posted: January/06/2010 at 07:52
Time will tell.  Wouter obviously has his mechanics down.  Let's see if my ASSumption pans out.  I am especting to see groupings of ruffly the same MOA as the 100 yards test.
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Direct Link To This Post Posted: January/07/2010 at 01:52
Thanks for some sanity and rescuing this thread.
The law of physics dictate that parallax error with a consistant cheek weld should produce the same consistant result. So if a shooter places his eye consistantly 3thou off the optical path he will achieve a consistant impact point in relationship to that error. By dialing the turrets he can shift the aimpoint to his impact point. This zeroed impact point/reticule aim point will only be correct at the distance it has been so zeroed.
 
Having said that, if a good shooter can maintain his eye in line with the optical path by correct cheek weld, the law of physics dictates that no parallel error excists, irrespective of the fact that the sight picture and reticule may be on different focus points. Parallell error only excists when the eye moves off the optical path.
 
This error can be calculated with mathematical formulas.
As an example, using a 20X power scope with a 50mm objective lens, the exit pupil is 2,5mm. The maximum the eye can be off the optical path is 1,25mm. Any further and the sight picture will be black. The scope has been set parallax free at 100m.
So to get back to JonA's suggestion of a 400 m test. The laws of physics dictates that the maximum parllax error can only be  1.25X20(400-100)/100 = 6.25cm or 2.5 inches in one direction. Should the shooter move his eye from one extreme end of the exit pupil to the other then this error doubles to 5 inches. The eye has to be exactly on the focal point for this calculation to be correct.
 
Can a good shooter manage better cheek weld and half this error by maintaining a better eye to optics path?
 
This is what I set out to do on a practical level and see what is possible. So far, for the 100m distance, this seems possible.
Can it be done at 400 m? My own shooting ability is about 1MOA at this distance, in other words with my scope at zero parallax at 400m and all systems firing, I should be able to hold a 4 inch grouping.
Can I still shoot a 4 inch grouping with the same scope but parallax set to 100m???
 


Edited by 8shots - January/07/2010 at 04:47
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Direct Link To This Post Posted: January/07/2010 at 06:29
Time to make some pudding, Wouter!
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Direct Link To This Post Posted: January/08/2010 at 05:08
Originally posted by 8shots 8shots wrote:

Nowhere in this thread did I talk about applying this information to any distance beyond 100m.

I'll give you that.  You hadn't yet, in this thread.
Originally posted by budperm budperm wrote:

He just likes to argue for the sake of argueing sometimes.

No I don't!!!!









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Direct Link To This Post Posted: January/08/2010 at 05:34
Originally posted by Jon A Jon A wrote:

[QUOTE=8shots]Nowhere in this thread did I talk about applying this information to any distance beyond 100m.

I'll give you that.  You hadn't yet, in this thread.
 
You must be having a weak moment!!!
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Direct Link To This Post Posted: January/08/2010 at 06:06
The proper reply Jon is.... Nuh-Uh!!! Laugh
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Direct Link To This Post Posted: January/10/2010 at 07:13
Ok, I made some pudding, now for the eating.
 
This Sat I managed to get to a longer range to try out the 400m stuff......well what happened????
 
These are all first targets and no repeats were shot. I made one attempt only.
 
First up I checked the 200m zero. The rifle was spot on. Whilst at the 200m mark I also focused the parallax setting on a 100 m distance and shot a grouping.
 
 
 
 
 
 
 
 
 
So far so good, both groups stayed under 3/4 MOA and would bring home the bacon.
 
At 400m :
 
 
 
Ta-daaa, both groups at 400m under 1MOA.
 
So yes, a consistant cheek weld that maintains the eye close to the optical path can  overcome parallax error.
 
I will however concede and agree with JonA (and this burns my >>>> to do this), that shooting accurately at the longer distances without being parallax free takes a lot of concentration and effort.
 


Edited by 8shots - January/10/2010 at 07:20
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