simplified :: how your scope sight works :

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  • Last Post 15 September 2015
Ken Campbell Iowa posted this 13 September 2015

i have noticed that most of my shooting friends are confused when adjusting their scope sights  for ” inner alignment ” ... so after trying a 15 minute lecture on lens theory and the corpuscular theory of photons ... and inducing mild coma mixed with future avoidance of myself ...  i now find the following simple discussion clears up the picture ( get it ? ) with happier results for all involved ::::

SIMPLY:: adjust the front lens so the target image falls sharply on the crosshairs.  then adjust rear eyepiece until the target/crosshairs are sharp.

1)  we are dealing with three things ::  front lens, AND  the reticle ( crosshairs ) AND the rear lens .

2)  for any given distance to the target the front lens forms a clear sharp image about halfway down the tube. 

3 )  the reticle is about halfway down the tube .

4)  the sharp image and the reticle must be at the same place halfway down the tube  ...either one can be moved forward or backward ..  the rear lens has nothing to do with this ... put it in your pocket ...    in most classic scopes you move the front lens until the sharp image is on the reticle  ... < in non-adjustable scopes the factory has guessed at this alignment for you .   usually very long distances > ...

5)  oh, the rear lens in your pocket .. it is just to look at the clear image that is halfway down the tube ... golly, and there is that crosshair ... you can see the deer and the crosshair both sharply focused together ... you can move your eye left and right and the crosshair and the deer are locked together !!

6)  again, the rear eyepiece is just to look at the mid-tube image and the crosshair at the same time ....  it doesn't look at the deer, it only looks at the midtube image, and the real crosshair .

7)   if you look through your eyepiece and the deer and crosshairs are not in focus at the same time ( and one moves differently than the other when you move your eye ) ... it is not your eyepiece,  >>>>>  your front lens isn't focused on the reticle .   the eyepiece can only make the image and the crosshair fuzzy or sharper, it cannot align the two ...

so we see that you ::  simply ::

adjust the front lens so the target image falls sharply on the crosshairs.  then adjust rear eyepiece until the target/crosshairs are sharp. 

hint :  when adjusting rear eyepiece for a sharp crosshairs, i point the scope up at the sky so i don't get distracted by the target . 

note a big hammer is not required .  ( g ) .

ken

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M. W. Curtess posted this 13 September 2015

Very Interesting! I don't hunt (only because I live alone and really can't use all the meat from even a small WT deer - and anybody I know already has more in their food freezers than they can use between deer-seasons). But I shoot as if it had a hunting application. I do OK with high-quality vernier tang sights on appropriate silhouette rifles, but pretty much need scopes for 100 - 300 yd. paper. Most of mine now have Adjustable Objective lenses - which when at maximum sharpness also eliminate parralax for that distance. What puzzles me is that most of my scopes play tricks with me when I adjust the rear (ocular?) lenses. When sharpest, either the vertical or horizontal cross-hair components are sharpest. I normally set them at a compromise to where both are about the same definition. But at that setting, neither is as sharp as is possible when the other is a bit blurred. I have never asked about this before - for fear that someone could tell me that there is something dreadfully wrong with my eyes (which is really bad news to anybody), but I've had this result for about 20 years and it hasn't got any worse, so now my curiosity dominates my concerns. Certain target scopes have etched fine-line crosshairs - and no problem with those. Does any reader have this experience - and an explanation for it?

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joeb33050 posted this 15 September 2015

Maybe it's me, but ... Scopes have a focus adjustment on the rear lens.

Spotting scopes, no crosshairs, adjust the rear lens so that the thing you're looking at is clear.

Scopes with crosshairs/reticle, adjust the rear lens-looking at the sky or a piece of white paper-so that the crosshairs/reticle is clear. Look away often-don't let your eye accomodate-you want crosshairs clear just as you glance at them.

Scopes with AO = adjustable objective (front) lens---this adjustment is for eliminating PARALLAX. Put the gun/scope on a stable rest-look at a target at ex 100 yards-move your head. If the crosshairs move on the target, left right up down-that's parallax. We make parallax go away by adjusting the objective lens, the front lens. (Except Feckers)Note that parallax and range go together, a scope with no parallax at 100 yards WILL have parallax at 50 yards. Change range and you must adjust objective. So, rear lens adjusts focus by making crosshairs clear, front lens eliminates parallax.

InfrequentlyWhen the rear lens is WAY out of adjustment, the front lens may be adjusted for no parallax but in the wrong place. Most AO scopes have marks showing where to set the objective lens for different ranges. 50 ft, 50 yds, 100 yds, 200 yds etc.WAY out of adjustment, maybe the front lens ex is set for no parallax at 100 yards but the lens is set on the 50 yard mark.Set the front = Objective lens at the correct = ex 100 yard mark-ya got parallax. Crank the rear lens until the parallax goes away. Right there the crosshairs and target will be in focus. No photons are required, it's all done with waves.

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joeb33050 posted this 15 September 2015

M. W. Curtess wrote: Very Interesting! I don't hunt (only because I live alone and really can't use all the meat from even a small WT deer - and anybody I know already has more in their food freezers than they can use between deer-seasons). But I shoot as if it had a hunting application. I do OK with high-quality vernier tang sights on appropriate silhouette rifles, but pretty much need scopes for 100 - 300 yd. paper. Most of mine now have Adjustable Objective lenses - which when at maximum sharpness also eliminate parralax for that distance. What puzzles me is that most of my scopes play tricks with me when I adjust the rear (ocular?) lenses. When sharpest, either the vertical or horizontal cross-hair components are sharpest. I normally set them at a compromise to where both are about the same definition. But at that setting, neither is as sharp as is possible when the other is a bit blurred. I have never asked about this before - for fear that someone could tell me that there is something dreadfully wrong with my eyes (which is really bad news to anybody), but I've had this result for about 20 years and it hasn't got any worse, so now my curiosity dominates my concerns. Certain target scopes have etched fine-line crosshairs - and no problem with those. Does any reader have this experience - and an explanation for it? I saw this years ago, either horizontal or vertical hair clearer than the other. On several scopes, when I was figuring out how the scopes worked-adjustments etc. I asked Loring Hall about it and he suggested I write down date, time and which was clearer. Back off the ocular = rear lens a turn or two before going home. Next time at the range, set the ocular and do it again. The effect was not repeatable. I soon convinced myself that the effect-one hair clearer-was not repeatable. Loring said that if for example the horizontal was clearer, then a slight adjustment would make the vertical clearer. It didn't on my scopes. But by then I had been looking through the scope too long-trying too hard.We kinda agreed that the effect was in my eye or brain, wasn't real.Loring told me that he had gone through the same exercise years ago.(This for Lyman STS, Unertl, Fecker, Litschert/Davis and GOOD internally adjustable scopes.)

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billglaze posted this 15 September 2015

I asked my optometrist one time about the single crosshairs situation, and he said it could be caused by a bit of astigmatism. I had that problem (along with others) and it went away after my cataract surgery. BTW: he is also a shooter in the same club to which I belong. If that means anything.

Bill

In theory, there's no difference between theory and practice. In practice, there is. My fate is not entirely in Gods hands, if I have a weapon in mine.

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