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Do all AO bell adjusters cause reticle wandering?

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calinb View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote calinb Quote  Post ReplyReply Direct Link To This Post Topic: Do all AO bell adjusters cause reticle wandering?
    Posted: July/16/2014 at 14:07
I have a Vortex Razor 5-20x50 and a Bushnell Elite 6-24x50 with side parallax/focus adjusters. When using these scopes, the reticles are always perfectly fixed and stationary in the FOV when I turn them though their entire range. (I have a Leupold Zero-Point so it's easy to test scopes for consistency and also measure the calibration accuracy of reticles and elevation/windage "click" adjusters, etc.)

I also have the following cheap scopes with AO bells. When I turn the AO, the reticles wanders though most of a circular arc in all of them (to some degree or another), resuting in significant shifts in POI / zero:

--------SCOPE---------------------------ELEV (MOA)------WIND (MOA)---
Hawke Sport 4-12x50___________6 ____________8
Hawke Panorava EV 4-12x50____~2 ____________2+
RWS 3-9x40__________________6 ____________8
BSA 2-7x32________________~1-1/2__________~2

I'll check my Vortex Crossfires when I get a chance too, but it would appear that bell AOs are of limited usefulness, requring re-zeroing with any significat adjustment! I'd love to hear from the experts, here, but it seems to me that the objective lenses might be "cocked" in their housing (not square with the optical and adjuster axis) to some extent, causing these deviations.

Maybe there's a discussion on this subject somewhere in the forums, but I could not find it.

Thanks,

-Cal
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calinb View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote calinb Quote  Post ReplyReply Direct Link To This Post Posted: July/18/2014 at 12:17
Update:

I checked my two Vortex 6-24x50 Crossfire scopes.

--------SCOPE---------------------------ELEV (MOA)------WIND (MOA)---
Scope #1_____________________~2 ____________~0
Scope #2______________________1 ____________<1

Not too bad, compared to the rest of the pack, but obviously adjusting one's AO bell can be a problem, depending on usage and how much it's turned. The circular movement the reticle against the field of view tracks the angular movement of the AO adjustment bell (adjusting from 30 yards to 130 yards creates a large and significant amount of reticle wandering around the circular "track" whereas going from 130 to 230 yards is much less).

Hawke customer service gave me an RMA number. I'm sending the Hakwe scopes to them for service. I expect that they will be able to reduce the reticle shift in my Sport HD, but perhaps not the Panorama EV, because it seems to be performing near the limits of precision for these AO bell adjusters. I also suspect that the side parallax adjustment system is a far superior design to the AO bell design. Hawke customer support also said that a poorly ground objective lens can cause this problem. That makes sense, but I suspect that lens alignment error is more likely to be the culprit and the manufacturing-limited weak link.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ol0ko Quote  Post ReplyReply Direct Link To This Post Posted: July/20/2014 at 16:13
So you are suggesting that the bell AO design in nature is flawed and the side parallax adjustment is superior. I guess it could be and to an untrained eye some one with a pretty good scope with an AO bell design could have some issues hitting the target?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote calinb Quote  Post ReplyReply Direct Link To This Post Posted: July/20/2014 at 17:08
Thanks for your reply to my post, ol0ko. I really thought this issue and my thread would generate more interest here and also some comments from the more experienced gurus. I'm beginning to think that few people have thought to investigate this source of error and the it just gets buried in the other errors associated with live fire testing.

Yes, I suspect the design is inherently inferior to the side parallax adjusters, but I'd like to hear from other users who have the means to measure this error. From a scope manufacturing and assembly standpoint, it seems to be difficult to hold the alignment of the objective lens sufficiently accurately to keep the reticle deviation to an insignificant level of error.

I have a friend who will check his Leupold Vari-X III AO for me, but it's difficult to accurately quantify the amount of reticle wandering, unless you have something like the Leupold Zero-Point tool. The zero-point received great reviews from users (as a sight-in tool), but has been discontinued by Leupold. You can try to point a scope under test at a target grid and strap it down securely, but it's very difficult to make it absolutely motionless during the AO adjustments. The nice thing about the Zero-Point is the inch/100 yard calibrated grid is right in the device and you don't have to even strap down the scope/rifle. You just have to make sure you don't bump or dislodge the position of the Zero-Point on the end of the barrel during scope testing.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Sgt. D Quote  Post ReplyReply Direct Link To This Post Posted: July/20/2014 at 21:31

I had hoped to see some response as well but, as you mentioned. There may not be much research on the issue. I think like myself most folk just find the adjustable objective to be a hassle to deal with compared to side focus. I have switched out all but one of my scopes to side focus. Mainly due to it being more user friendly. If it proves to be a superior system all the better. I suspect that the adjustable objective may be on its way out. Can't say that that would cause me any since of loss.

Hope you find the info your lookin. Unfortunately its not an area I have researched.

If I hadn't said so before, Welcome to the OT.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Sparky Quote  Post ReplyReply Direct Link To This Post Posted: July/20/2014 at 21:58
Originally posted by calinb calinb wrote:



Yes, I suspect the design is inherently inferior to the side parallax adjusters,



I have one Swarovski, three Leupold's and one Nightforce all with AOs. And I see none of the issues you are talking about. If it was an inferior design I seriously doubt Swarovski would be using it or for that matter Leupold or Nightforce.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rancid Coolaid Quote  Post ReplyReply Direct Link To This Post Posted: July/21/2014 at 12:16
I have used very good quality optics with parallax at the bell (Swaro and USO comes to mind) and not had this problem.

My guess, and this is just a guess, is that if you get a few equally inexpensive side-adjust, you would see some manner of problem with them too.

Comparing well made, not inexpensive side adjust with very inexpensive front adjust isn't really a fair comparison on many levels.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote cheaptrick Quote  Post ReplyReply Direct Link To This Post Posted: July/21/2014 at 12:23
I've always believed, (maybe incorrectly), that AO's were "better" than a SF due to the fact that there were less mechanical parts with an AO, thus less prone to failure. 

I prefer AO's to SF because I'm a Lefty. As already stated above, I have had some AO scopes and SF scopes and never had a problem with either....either. Bucky  


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Post Options Post Options   Thanks (0) Thanks(0)   Quote ol0ko Quote  Post ReplyReply Direct Link To This Post Posted: July/21/2014 at 15:07
Originally posted by calinb calinb wrote:


Hawke Sport 4-12x50___________6 ____________8
Hawke Panorava EV 4-12x50____~2 ____________2+
RWS 3-9x40__________________6 ____________8
BSA 2-7x32________________~1-1/2__________~2



These are the sort of scopes an airgunner would use and besides the two hawke scopes these are cheap scopes and I would not be surprised if the bell AO design in these are flawed. I am surprised though with the hawke scopes you mentioned. Many people are under the impression hawke makes good scopes and indeed they do but if there AO bell parallax design is flawed in them then that changes a lot in my perception of them.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Sparky Quote  Post ReplyReply Direct Link To This Post Posted: July/21/2014 at 17:43
Just wondering, but what happens when you shoot an actual five round group rather than use your bore sight? And are you sure you are not moving your head while doing this? Also I don't understand why you would want to change the AO setting at a certain distance once it is adjusted properly. Plus if the AO is not set correctly when you move your eye the reticle will move on the target. If your AO setting is closer than the actual target the reticle moves in one direction and if it is farther than the target it moves the other direction in relation to which way you are moving your eye. Or to put it another way when you move your eye the reticle moves the same direction or opposite direction depending on your AO setting being closer or farther away. But if your AO setting is correct for the distance the reticle does not move even with moving your eye.

In my experience using a bore sight is good for nothing more than getting on paper and is no substitute for actually shooting a group.

If your reticle is indeed moving when you are adjusting your AO you have a defective scope. Since to my knowledge the reticle is not part of the lens group that are affected by adjusting the AO.


Edited by Sparky - July/21/2014 at 17:48
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Post Options Post Options   Thanks (0) Thanks(0)   Quote koshkin Quote  Post ReplyReply Direct Link To This Post Posted: July/21/2014 at 17:58
AO is not inherently inferior to SF.
 
$100 scopes are inherently inferior to $1000 ones.
 
From the design standpoint both work well barring a QC issue.
 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Gerry Atric Quote  Post ReplyReply Direct Link To This Post Posted: July/21/2014 at 18:58
A question regarding the bore-sighter:

What will happen if the barrel crown is canted or damaged?

I suppose that will have an impact on meauserment accuracy?


Gerry Atric
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Post Options Post Options   Thanks (0) Thanks(0)   Quote RifleDude Quote  Post ReplyReply Direct Link To This Post Posted: July/22/2014 at 13:54
I've had several A/O scopes and have never seen this issue with any of them. Then again, I've never owned any cheap A/O scopes either. If you're seeing deviations in reticle position relative to the grid on a bore sighter, the shift you're seeing may be simply due to extreme parallax, as the scope is unable to compensate for parallax that close. If your eye isn't exactly centered in the center axis of the scope, you will see an apparent shift as you move the A/O.

The only way to know for certain you have a problem is to shoot groups on paper at distance, move the A/O between group strings and see if there is an actual POI shift. If what you're seeing is an actual mechanical shift in reticle position relative to the bore sighter grid, then there will be a huge POI shift well beyond normal shooter error and rifle/ammo system deviations down range.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Kickboxer Quote  Post ReplyReply Direct Link To This Post Posted: July/22/2014 at 23:55
I bought a 10-50x56 NcStar to play with just for a comparison vehicle.  It has AO and the "moving reticle", which I have dubbed the "Mad-eye Moody Effect".   There is a POI change with the AO movement, but it is inconsistent... sometimes POI change is large, sometimes it does not occur and I've found no rhyme or reason to when and how it occurs.  I've chosen to not waste ammo determining the parameters.  I sometimes use the scope as a spotter, and it is OK at that.  It will probably become one of my "Hathcock shot" test units.  I paid very little for the scope at a gun show and it has given me enough use to pay back investment.  When I shoot the scope with either 338 LM, 378 WbyMag, or 50BMG, it will be well worth it.  I suspect 50BMG with AP might do the job of going all the way through... maybe.  What I really need for the test is a WWII PU 4x rifle scope. Can't find one that isn't more expensive than I want to pay for a scope to put a bullet through. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote calinb Quote  Post ReplyReply Direct Link To This Post Posted: July/23/2014 at 00:14
Wow--this thread is heating up!  Thanks for your posts and help, everyone.

Sparky, Rancid Coolaid Cheaptrick,
I guess the more expensive AO scopes are built on better manufacturing processes that produce the objective alignment necessary to prevent significant wandering. I don't think the AO design is inferior to a side adjuster, if you can build it right and I should not have said that AO is inherently inferior. As Cheaptrick pointed out, AO seems to be simpler than side adjust. It may be more expensive to assembly AO correctly however. I don't really know for sure. My two side adjust scopes are expensive, relative to my AO scopes, and they are perfect in this respect.

Sparky, 
I started my investigation after I shot my Hawke Sport HD to get on paper at 25 yards or so and then noticed a large POI windage shift when focusing and shooting out at 100+ yards (and there was no wind).  Yes--the scopes are defective--particularly the Sport HD! If the objective lens and AO bell axis are not aligned with the optical axis of the scope, the image will shift relative to the reticle as the objective lens turns. As Hawke customer support pointed out, it can also occur with an imperfectly ground lens, but all of the shifts I measured follow a circular path as the objective is turned (except maybe the one Vortex, but the two Chinese Vortex scopes were the best of the bunch). The circular path is consistent with the alignment issue.

If you are shooting at targets over a variety of ranges, you adjust the AO in the field to eliminate parallax. Unfortunately with this problem, you have also destroyed your zero in both elevation and windage because the reticle has shifted independent of any parallax error. The zero is only good when the AO bell is set identically to how it was set when the scope was zeroed. Changing the AO setting requires re-zeroing the scope (or dialing windage and elevation corrections/dope for each AO setting).

Sparky, RifleDude,
My eye position was fixed sufficiently to not cause a parallax shift. Furthermore, the characteristic circular path is absolutely repeatable when viewed across the Zero-Point background grid. You can just watch the cross hairs move in a circle, which would not be the case for wandering caused by changes in eye position. I found that Parallax was not an issue or even a source of even measurable error with the Zero-Point image. (To check, I deliberately tried to provoke it by moving my eye and it required a huge change in head position to even see it against the grid.)

Gerry Atric, 
Because I did not move the Zero-Point device during any of the tests, issues related to its alignment on the barrel were not a factor. I was only interested in the shift of the reticle and not trying to duplicate a previous setting or zero. Yes--the Zero-Point's usefulness for resetting/re-establishing a previously recorded zero is limited by one's ability to attach the device to the barrel consistently. Contrary to what you might intuitively expect, it is quite insensitive to up/down and right/left placement on the barrel but it is extremely sensitive to inconsistent angular placement (cocking it off of square). If the barrel crown is damaged or not circularly symmetric, the sensitivity is more of a problem! I have found it to be more difficult to consistently attach the Zero-Point to an 11 degree crown than a crown that offers more flat surface area square with the bore. Regardless, these challenges did not affect my measurement because I was only interested in the shift of the reticle and, even if a test is duplicated and the Zero-Point is re-attached somewhat inconsistently, that measured shift is always the same and along the same characteristic circular path.

koshkin,
Yes--from what people are reporting here, this seems to be a cheap scope problem rather than an AO problem. I don't have a collection of both cheap and expensive AO and "sidewinder" scopes to check, so that's why I asked here!  Thanks to all for helping me to answer the question.

All,
Besides sighting-in (its intended and marketed purpose), the Zero-Point is a very useful tool for measuring reticle features and elevation windage dial click calibration too! You can easily determine if clicks are as spec'ed by the manufacturer. For example, it's easy to discover that many scopes have dials marked as "1/4 MOA" but they are really 1/4" @100 yards (or vice versa). There is nearly a 5% difference between the two. both my Hawke Sport HD and Panorama EV have Hawke "10x mil-dot" reticles, which means they are supposed to be calibrated at 10x zoom magnification. It turns out that my Sport HD must be set to about 10.5 and my Panorama EV must be set to 9.5x to obtain mil spacing in the reticle. These kinds of investigations might be the Zero-Point's most useful application, because it's not terribly difficult to get on paper using more traditional and less expensive methods without it!

Hawke Sport Optics gave me an RMA number.  Both scopes should be in their service center now.  I'll let everyone know how they do once they are returned to me.  BTW, I've done plenty of A/B comparisons of these scopes and others in my inventory. The Panorama EV offers an exceptionally clear and sharp image and the illuminated reticle is very nice for the price. I hope they can get the AO working better.

-Cal
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Post Options Post Options   Thanks (0) Thanks(0)   Quote calinb Quote  Post ReplyReply Direct Link To This Post Posted: July/23/2014 at 00:16
Kickboxer,

Now I know what to do with my RWS scope (from an air rifle "combo")!Big Grin
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Post Options Post Options   Thanks (0) Thanks(0)   Quote calinb Quote  Post ReplyReply Direct Link To This Post Posted: July/23/2014 at 00:24
I forgot to mention one other trick you can do with a Zero-Point. You can use it like you might use a "zeroing gun vice" or Shepherd 1st+2nd focal plane reticle scope. Because the Zero-Point reticle is visible along with the target image, you can place the Zero-Point grid "cross-hairs" on the point of aim while you dial the scope reticle cross hairs to match the POI on the target.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Oldtrader3 Quote  Post ReplyReply Direct Link To This Post Posted: August/13/2014 at 22:59
I think that a shooter needs to check parallax at the different AO settings because the settings in either the AO or side parallax adjustment may not be accurate?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote billyburl2 Quote  Post ReplyReply Direct Link To This Post Posted: August/17/2014 at 15:03
Check how much the reticle moves across the grid when you change the mag range on your sfp scopes...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Urimaginaryfrnd Quote  Post ReplyReply Direct Link To This Post Posted: August/17/2014 at 15:22
I do not still have any front parallax adjustment scopes all mine are side focus or the rear focus SS or they have no adjustment like an ACOG or Aimpoint. I have had some in the past never a really cheap one but I had an 8x Weaver that was on my grandfathers rifle and it seemed to function properly but that was years ago. I just never really liked having the adjustment in front and was really thankful when things started going to side focus. Sounds like scopes that could be traded for something more useful at a gun show.


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