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Thread: Optically centering crosshairs

  1. #1
    Marksman

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    Default Optically centering crosshairs

    I was shooting the other day, I removed my scope to change calibers on my FX Crown, and upon centering the scope I ran into the end of adjustment on the elevation turret. I have now bought some mounts from Rashaad that can be adjusted, but this had me thinking. If one adjusts parallax it is to focus, but also to have the crosshairs stationary on the target when you move your eye.
    So when the parallax is set perfectly, the scope will be in focus and when you move your eye behind the scope the crosshairs remain on the target, but if the crosshairs are at their max adjustment or close to max, does this not have an effect on accuracy as the crosshairs are not in the middle of the glass lenses, and the quality of the image might suffer? Maybe even the parallax? I know some shooters prefer the holdover technique, which would allow the crosshairs to remain optically centered. I would really like to know from the more experienced guys on here. Aren't we all ever searching for the ultimate accuracy?
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  2. #2
    Marksman

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    For those that wonder how to optically centre crosshairs, apparently turning the turrets to their extremes and finding the centre is a big no-no, although that is exactly what the Hawke manual tells you to do. I did mine by making 2 v-blocks and laying the scope body in them and turning the scope while looking through it and adjusting the turrets until the crosshairs do not move off the center point when turned.
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  3. #3
    Protea FT Team '12/'16/'17

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    You can do it on the rifle without having to take it off.
    put your rifle but against a wall. shine a light from the front of the scope and you will see two cross hairs on the wall. adjust the turrets till you can only see one. this is then the optical center.

    you need to adjust the paralax and optical ring etc to get the image as clear as possible. etc
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  4. #4
    Marksman

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    Thanks for that info Total SS, one is never to old to learn new tricks.
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  5. #5
    Protea FT Team '19
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    Quote Originally Posted by Cutler View Post
    If one adjusts parallax it is to focus, but also to have the crosshairs stationary on the target when you move your eye.
    The terms "focus" and "parallax" have become interchangeable over time as people refer to them as the same thing. However, strictly speaking, "focus" is almost a by-product of setting the parallax.

    Quote Originally Posted by Cutler View Post
    So when the parallax is set perfectly, the scope will be in focus
    Depends on your eyes. A scope that has its parallax set perfectly can be out of focus for some people.
    With my junk eyes and some of the higher-mag Hawke scopes, I'd find that when shooting a 25m target, I'd have to set "focus" to about 27m in order to get the parallax correct. So the target would be slightly out of focus, but the parallax was 100% (which is more important, IMO.)

    Quote Originally Posted by Cutler View Post
    and when you move your eye behind the scope the crosshairs remain on the target
    Yes.

    Quote Originally Posted by Cutler View Post
    but if the crosshairs are at their max adjustment or close to max, does this not have an effect on accuracy as the crosshairs are not in the middle of the glass lenses, and the quality of the image might suffer? Maybe even the parallax?
    Yes. Hence the practice of optically centering the scope before mounting it.

    Quote Originally Posted by Cutler View Post
    turning the turrets to their extremes and finding the centre
    That's what we refer to as mechanical center. While not as good as optical center, it's better than using turrets at the extreme end of their adjustment.
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  6. #6
    Marksman

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    I have one of those Hawke 10-50 x 56 Sidewinder scopes, will crank it up to 50 mag and see if the distance on the wheel where the scope focuses correspond to the rangefinder distance.
    Last edited by Cutler; 06-01-20 at 15:53.
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  7. #7
    Sharp Shooter

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    Hi Cutler,

    Yes please do that!,

    Looking for more info in that range of scopes as well as good old fashioned feedback from real, actual users.

    I have 2 x Hawke 4 16 50 Sr Pro Scopes and was/ am /wanting / needing a bit more for my tired old eyes,!!!
    Currently they are mounted on an LGU Master ���� and HW98, respectively.

    Regards Henry
    Quote Originally Posted by Cutler View Post
    I have one of those Hawke 10-50 x 56 Sidewinder scopes, will crank it up to 50 mag and see if the distance on the wheel where the scope focuses correspond to the rangefinder distance.
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  8. #8
    Protea FT Team '19
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    Quote Originally Posted by Cutler View Post
    I have one of those Hawke 10-50 x 56 Sidewinder scopes, will crank it up to 50 mag and see if the distance on the wheel where the scope focuses correspond to the rangefinder distance.
    R10 says it won't. And it won't because the rangings / distance markings on the sidewheel are set by a machine, and are probably in yards. You would need to create your own markings on the sidewheel in order for them to be correct, and even then other people may find them a bit "off".

    Perhaps I didn't explain clearly. If I focused the scope at 25m, the scope picture would be clear, but there would be a slight parallax error. If I focused the scope on a 27m target, then the parallax error at 25m would be gone.
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  9. #9
    Springer FT World Champion '09
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    Quote Originally Posted by Mark_F View Post
    R10 says it won't. And it won't because the rangings / distance markings on the sidewheel are set by a machine, and are probably in yards. You would need to create your own markings on the sidewheel in order for them to be correct, and even then other people may find them a bit "off".

    Perhaps I didn't explain clearly. If I focused the scope at 25m, the scope picture would be clear, but there would be a slight parallax error. If I focused the scope on a 27m target, then the parallax error at 25m would be gone.
    What do you mean?
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  10. #10
    Marksman
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    What I have done (mirror trick not working on my scope).

    Is to go to the scope specs.
    Check the MOA adjustment listed for your scope.

    My hawke SR pro had 53MOA of adjustment listed for windage and elevation.
    1/4 MOA per click.

    Thus 1/4 x 53 = 212.
    Centre should be 106.

    I would turn to one side and max it out but not force the turrents.
    Then you only have 106 clicks to turn back.( most scope have interval markings - like the hawke 4 click interval - 106/4 = 26.5 interval turns)
    I've tested this and it works ( every scope is slightly different to the manufactures specs but this will get you within a few clicks of optical centre).

    Bit of a hassle but better than maxing the turrents out left to right, losing count of how many clicks and having to repeat this process again.
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  11. #11
    Sharp Shooter

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    I am by no means an expert on this, but should we not be separating optical and mechanical zeroing?

    P.S. THIS still remains my most referenced link when I am troubleshooting problems. It is a sticky under the Optics forum as well.
    Last edited by Boerkwas; 08-01-20 at 13:35.
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  12. #12
    Sharp Shooter

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    I have an old Delrin V-Block setup that I threw together years ago somewhere - used it once, and I think it is in the back of a cupboard somewhere. If anyone wants to use it, they are welcome.
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  13. #13
    Marksman

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    I am certainly not an expert, that is why I enroll the collective knowledge of this fine forum, in my understanding mechanical zero as achieved by turning the turrets to their stop and finding the middle, optical zero as found by turning the scope in V-blocks (or using a torch to project the crosshairs on the wall like Mark F suggested)
    In my mind these two methods should yield very close to the same zero unless the scope is of questionable quality. I am going to remove my scope and do the experiment to see how far these 2 zeroing methods are apart. I am almost thinking that if you zero the scope optically it would be the gold standard, the true zero with the crosshairs in the middle of the lenses.
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