Optically Centering a Scope

[rsterne]

RE the "mirror method", a question and a few comments.... Doesn't it rely on the outside rim of the objective lense being perfectly square with the centerline of the scope?.... I've checked a few scopes to see how square the front is to the tube, and some are good, some are out by quite a bit.... I have one (a $200 scope) where if you put a Machinists square on the front of the Objective and then measure from the square to the tube just in front of the turrets, the difference is about 0.080" (2mm).... To me, that means that the reflection of the crosshairs would not align with the crosshairs by half that amount (eg. 0.040" or 1 mm) over a distance of 7 inches.... Over 100 yards (3600"), that would be 3600/7 = 514mm or about 20".... That would be about 80 clicks off center, by my calculations.... Not only that, but rotating the Objective may or may not cause the reflection to "walk around" in a circle, depending on if the lack of squareness is in the rotating part of the bell or in the threads that it rotates on....

It would seem to me, therefore, that using a mirror to center the crosshairs "optically" may not be the best method.... If the Objective is not square to the tube, I would think that the mirror, likewise, would not reflect the image of the crosshairs straight back down the center of the optical path.... Counting clicks relies on the manufacturer centering the parts in the tube properly, which may or may not be the case.... That leaves us with rotating the scope in vee-blocks bearing as far apart as possible on the tube as likely being the best method, IMO....

Bob

[sholo]

To be honest, I've never used the "mirror method" of centering a scope before (although I have read about it) and I definitely never gave any thought as to how square the objective rim was in relation to the tube. Normally I just count how many total clicks of adjustment I have (both windage and elevation) and set the scope at the halfway mark as a starting point. I then set a target up at 50 yards, usually a large piece of paper (old blueprints from work are great as they are about 2' x 3'), take a few shots to see where it's hitting and then shim the scope for elevation to get it as close as I can, then fine tune with the turrets. Not sure how to properly shim it for windage though, other than adding a shim to one side of the mount where it attaches to the rail? I don't know if this is the right way of centering a scope (or if it's even necessary), but it's how I've been doing it and seems to work OK for me, but then again I'm no sniper by any means, so....????

[blkexp98]

I know this is an older thread but I didnt have much luck when I tried to use the mirror method. How I do it is put the scope tube on V blocks and aim at a reference point. Then what you do is adjust the scope so the crosshairs dont move on the point with a full 360 degree rotation. The easiest way is to set one axis at a time rotating it only 180 degrees and then check the final result with the 360 degree rotation. I have much more confidence in the tube being right vs the objective.

[Garththomas]

I used to use the mirror method but it's been shot down just about everywhere so now I use the fruit basket method, they are about the right width and I just cut a couple V-notches then adjust accordingly.