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Eliminating parallax with non AO scope.

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/18/2009 at 20:39
Dave Wilson View Drop Down
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I've shot a fair amount of long range the last few years and my technique for eliminating parallax with a scope that doesn't have any AO adjustment has been to back out of the scope till a black ring appears and center this with the outside of the tube and the crosshairs. it seems to work. was wondering if this technique is correct for eliminating parallax?
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/19/2009 at 08:34
Dale Clifford View Drop Down
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your not giving the distances your shooting. the eye has an amazing ability to center things as anyone who has used peeps or ghost rings knows. question depends also on the objective size, size of target, but in general, the more the shooter is behind the optical axis the less the error will be. By the way I use this same technique in getting reticles aligned when mounting scopes.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/19/2009 at 19:09
Dave Wilson View Drop Down
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i don't understand where the distance that's being shot has anything to do with what i'm asking. i want to know if centering the black circle will eliminate parallax at any range.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/19/2009 at 19:11
Dale Clifford View Drop Down
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no
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/19/2009 at 20:05
Dave Wilson View Drop Down
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why not?
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/20/2009 at 09:11
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Eliminating a nice, crisp sight picture around the outsides of your FOV in a scope by backing out until you are past the intended eye relief isn't really a good idea for consistant shooting. 
 
Some scopes are more forgiving than others, but if you are serious about shooting long range and not having an AO is bothering you to the point where you are trying different techniques than others it might be that time to invest in a new scope.
 
I know that this isn't exactly what you wanted to read, but it's just my opinion, take it for what its worth, or leave it.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/20/2009 at 09:49
Dale Clifford View Drop Down
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moving back are forward does not change the fact that the image from the objective lens is not coincident with the reticle.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/20/2009 at 15:04
Dave Wilson View Drop Down
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i understand what you're saying. that similar focus is what makes an inconsistant eye position relative to reticle not mean anything. in my opinion, if you can look at the reticle in the same position each time, you can accomplish the same thing. this is what i believe centering the reticle in the field of view does.
   my one experiment with this seemed to prove it. again, i only did this once, with one scope. i shot at 2 targets at the same, round robin. centering the cross hairs on one target and intentionally moving my head about the field of view on the other. one 5 shot group was a little under 4" and the other weren't all on the target! this was at 600 yds.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/20/2009 at 20:27
Dale Clifford View Drop Down
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but-- you don't know which side of the lens its not coincident. correct optical alignment is only that just looking down the center, I think your assuming causality when there is only correlation.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/21/2009 at 01:24
8shots View Drop Down
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Dave, my thoughts are that yes, you may achieve a consistant shot placement in this manner. However the further or closer you move from your zero distance, the more your impact point will shift.
In other words inconsistencies may be avoided, but the parallax still excists and you may be looking at an angle towards your target.


Edited by 8shots - December/21/2009 at 01:38
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/21/2009 at 02:22
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I'm sure that what you are doing is helping you sight through the scope more consistently and is indeed a band-aid fix for parallax.  We took several scopes out one day and with a benchrest, we checked parallax on them all.  The scopes were all mounted on rifles and we rested the rifles without touching them, then moved an eye up and down/left to right while looking through the scope at the correct eye relief. 

We also had a Kahles 3.5-10x50 AH,  Kahles 3-10x50 CL, Kahles 4-12x52 CL, Zeiss Conquest 4.5-14x44, Leupold 3-9x33 VX-II. All had side focus except the leupold and Kahles AH which had no AO or side focus.  The two without focus devices seemed to find their "no-movement" spot between 100-150 yards, so we used the side focuses on the others to dial them in at those distances for comparison sake. Keeping all the same settings, we looked at a target that was 600 yds out, all of them set on 9x. 
 
Most of them had tremendous target-to-crosshair movement between 8-10 inches.  I've read that smaller objectives have less parallax, and the little Leupold 33mm did have the least, (can anyone back up that myth/fact?)
 
We cranked up the side focus knobs (on the 3 scopes that had them) and pretty much eliminated all of the movement. This sold me on scopes that have side focus or adjustable objective.  At least on medium to high power scopes.  We might have had better results if we had tested at 6x instead of 9x, but who buys a high power scope and then shoots 600 yds on 4x???
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/21/2009 at 06:35
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T-brake, it is not a myth. The amount of parallax error is a function of the objective lens. The larger the objective lens, the larger the potential error.
Put differently, the error can never be greater then the size of the objective lens.
 
The question remains if parallax can be compensated for by having a "ghost" black ring of equal size around your sight picture?
In my opinion this will place your pupil in the centre of the exit pupil or scopes optical path. But let us assume the scope was poorly mounted and the reticule is no longer in the optical center of the scope after zeroing the rifle? This would result in an out of alignment sight picture, which would give consistant groupings, but a imnpact point that would vary as the shooter moves closer and further away from his zero point. That is to say left or right or higher and lower other then that which can be attributed to the normal ballistics of the bullet.


Edited by 8shots - December/21/2009 at 06:38
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/21/2009 at 06:42
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What the readers should realise is that T-brakes test checked out the maximum error, which only came to 8-10 inches at 600yds.
Now if a half decent shooter halves that error with proper cheek weld, he is looking at 4 to 5 inches at 600 yds, which is under 1MOA.
I think that any of those scopes without AO will perform better then most shooters hold ability.


Edited by 8shots - December/21/2009 at 06:43
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/21/2009 at 14:52
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I don't really agree with that line of thinking.  If additional variability is added by the scope, rifle or ammo, whether the shooter can hold 1 MOA or 1/2 MOA or 1/4 MOA or 2 MOA, he's going to do better with equipment that reduces the added variability to zero.  Actually in this specific case, the really good shooters will probably have less added to their group size than the less experienced.  But all will likely experience an increase in group size vs. using a scope with zero parallax at that range.

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.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/21/2009 at 21:15
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Yeah, I'm probably making too big of a deal about this, but I like to eliminate as much device error as I can because I know I'm gonna have a pile of human error Excellent

And we all know that you can't just take all of your errors such as parallax, rifle inaccuracy, human error, and average them, you have to add them all together. If your rifle will shoot a 1.5 inch group at 100 yds, your scope has 8 inches of parallax at 600 yds, and your gun is  clamped dead-still in a vise (no human error), your gear has enough error to shoot a 17 inch group at 600 yards, and thats not even considering wind, temp, and human error.Big Smile  Use a gun that will shoot a half inch group, and your error is still 11 inches...
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/22/2009 at 01:57
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JonA & TBrake, I agree with the above sentiments. My own equipment is tuned for the smallest possible error.
But the thread is about eliminating parallax without an AO..or making do with the equipment at hand.
The message I was trying to convey is that often a shooter makes too big a deal of equipment limitations. For example the scopes as illustrated above is capable of less then 1MOA error, yet the shooter may be shooting only to 2MOA error.
As you stated, the more experienced shooter will have less error added......and that was my point.....make sure your own ability is properly honed before starting an equipment race.

Edited by 8shots - December/22/2009 at 04:32
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/22/2009 at 06:53
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Originally posted by 8shots 8shots wrote:

.....make sure your own ability is properly honed before starting an equipment race.
 
That statement could answer a plethora of questions here.Excellent
 
Doug
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/22/2009 at 07:05
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Another thought on parallax and the actual contribution to field or tactical accuracy....
 
I have the Leupold 8,5-25 with side focus. On a tactical shoot we are expected to hit six inch targets from 200 out to 400m, within  a limited time. Due to time constraints most shooters (and I do the same) will midrange focus, say 300m. From there we just engage all the targets, without fiddling with focus or parallax adjustment.
 
For benchrest accuracy, a parallax adjustment is essential. For the rest I am not so sure. If I buy another tactical scope, I would pay little notice to AO features.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/22/2009 at 14:00
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I'd agree with that up to 10 power or so.  For example the 3-9 SS does very well with out it it situations like you describe.

I don't for higher powered scopes.   I have zero interest in a 14X or higher without some form of parallax adjustment.  In your example, you were able to set the scope at 300m precisely because it is adjustable.  Try setting it at 100 next time and I think you'll find the 400 yd targets very difficult at anything much over 10X.  So if you paid little notice to AO features and ended up with a fixed parallax scope set for 100M (as many European scopes are) you might not do very well.  Now if you get one set for 300 it won't be too bad at distance but your groups at 100 might really suffer (depending again on how high the power is) which may make load developement a PITA as many people don't have easy access to a 300 yd range. 

Though if you do have easy access to a 300 yd range that may not be too bad a compromise up to 14X or so, especially for a hunting scope somebody wants to keep light and compact as possible.
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