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Adjusting reticle vs. Adjusting mounting - Burris Zee rings

 
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  #22  
Old 10-08-2012, 01:47 PM
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Re: Adjusting reticle vs. Adjusting mounting - Burris Zee rings

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Originally Posted by green 788 View Post
Lots to "clarify" here.

The erector has it OWN lenses... and they take in light from the objective lens, and transmit it to the occular lens. The position of the erector has absolutely nothing to do with optical clarity.

And it's a good thing for us long range shooters that it doesn't... because we typically run the optic at a 100 yard zero, and dial up from there. We'll dial from bottom to top... but again, as the erector moves, it's only moving a few thousandths of an inch in each direction, and it's never going to be pointed toward the edge of the objective lens--and its transmission of the exit pupil (beam of light) to the occular lens will generally be centered--never toward the edge of that lens either…

…But the notion that moving the erector away from its centered position is going to harm clarity of the scope is simply not true... because the erector's lenses move with it, and the only lenses that don't move with the erector are large enough that the miniscule movement of the erector isn't going to point anywhere close to the lens edges--even if you dial it all the way to any extreme…


If you're wanting to split frog hairs... you could probably in a laboratory find some loss of clarity as you move toward the limits of erector travel...

However, for all practical purposes, you won't see it. Not unless you have a really cheap scope. :o (and maybe not even then)...

…I put a 40 MOA base on my .338 Lapua Mag... the Leupold Mk4 scope has to be dialed all the way down in order to get to my 100 yard zero (I think I've got about a dozen clicks (3 MOA) left of down-travel when I get to my 100 yard zero.

And I have honestly never noticed any compromise in optical quality at 100 yards, or at 1000 yards... or even with the turret topped out for 1 mile zero... the scope looks the same to me…

…One last thing... the depiction of the bottomed out erector shown above it certainly exaggerated for effect... it doesn't move that far, with that much of a slant... it actually only moves around 40 thousandths of an inch in any direction from center, depending on the scope.
Increasing the elevation does not change the location of the light rays on the objective lens. It changes the incidence angle of the light rays on the objective lens. In either case, the light rays always fall uniformly over the entire objective lens.

The erector lens movement is much larger than you indicate. The focal length of the objective lens for a typical long range rifle scope is 6-9”. For an average 7.5” focal length objective, 30 MOA of elevation change corresponds to 0.15” of turret travel, not “40 thousandths of an inch”. Some scopes have over +/-50 MOA of travel, which corresponds to about +/-.25”.

Burris Signature Rings can provide up to about 17 MOA (30 mm) or 25 MOA (1”) of correction. That is usually enough elevation bias for most shooters to get out to 1,000 yds.

In your case of the .338 Lapua, a mile shot requires about 60-75 MOA of elevation from a 100 yd zero, depending on the specific altitude, inclination, BC, MV, etc. By using a 40 MOA base, you are reducing that elevation requirement to 20-35 MOA from the optical center of the scope. As other posts have stated, this is a good approach for multiple reasons.

At an incidence angle of about 30 MOA, you would need a trained eye to notice the image blur due to off-axis aberrations in the objective lens. It does not, however, require an optical laboratory to observe this level of image blur. One way to observe this effect is to set up two identical scopes, one with an optically centered reticle, and the other with the reticle shifted 30 MOA. Then look through them at a target about 50-100 yds away. The target should be high up off the ground to minimize turbulence-induced image blur. Any person with good visual acuity would notice the difference in resolution and contrast in one scope vs the other instantly. It’s not “splitting frog hairs”. It’s an obvious effect if you do the side-by-side comparison. It will be observed with just about any scope at a price point below $1,500 due to the wide use of simple achromatic doublet objective lenses.

Under many shooting conditions, however, shooters may not notice the image degradation, even though it’s there. Trying to assess optical performance at a shooting range, for example, can be very misleading because the image resolution and contrast are usually limited by turbulence in the air, not by the optical performance of the scope.
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  #23  
Old 10-10-2012, 03:44 PM
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Re: Adjusting reticle vs. Adjusting mounting - Burris Zee rings

Thanks for all the input/feedback, guys. I've learned a lot from your answers and the general "debate". Many good points about starting with biased mounting and changing image quality due to reticle adjustments. The latter is something I hadn't thought about until recently, despite my lifelong involvement in photography, cinematography, and optics. I'm about to build it all up tonight and shoot this weekend.

I should note that the 1" Burris Sig Zee rings did NOT come with the elevation inserts as the phone consultant at Big C told me they would. (You were right, Bruce.) Looks like I'm going to have to order them from elsewhere because they're not even listed in their online catalogue. We'll see today if they compensate me somehow for false information. If not, I will yelp them a negative.

I needed to build this rig on a pretty tight budget, so $500 was the limit for the scope..."mid-low end" as described by some here. Only 35 MOA of adjustement is part of why I started this thread. Nevertheless it should serve me well for the time being. I was also concerned that a full 20 MOA rail would put me so high at 200 that even at the bottom of the scope adjustment range I might be above my prefered zero. So with the Burris sigs I have some intermediate choices.

Thanks again for all the helpful info!
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  #24  
Old 10-10-2012, 04:11 PM
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Re: Adjusting reticle vs. Adjusting mounting - Burris Zee rings

Not sure if you can fit it in the budget but Burris makes an insert kit that gives you many options to choose from, I think .005, .010. 020 for the 1 inch set. If you think you may end up with other signature rings down the road you can use them in those as well.

Good Luck!

Scot E.
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  #25  
Old 10-10-2012, 04:34 PM
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Re: Adjusting reticle vs. Adjusting mounting - Burris Zee rings

Quote:
Originally Posted by Scot E View Post
Not sure if you can fit it in the budget but Burris makes an insert kit that gives you many options to choose from, I think .005, .010. 020 for the 1 inch set. If you think you may end up with other signature rings down the road you can use them in those as well.

Good Luck!

Scot E.
Yes, I am ordering them. I figured the same about using them in the future on other rifles I hope to get. But due to near term limited shooting opportunities and me chomping at the bit to break this thing in, I'm just going to mount with the 0 MOAs tonight.
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