Understanding Parallax & its Effects

Forums Knowledge Center Understanding Parallax & its Effects

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    Michael
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    Keymaster

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    sendler2112
    Participant
    Member

    A good place for me to copy the post I made on another thread concerning the adjustment of the ocular.

    A common method of adjusting the ocular is to set the parallax on infinity with the ocular lens turned in all the way.

    Point the scope at a white wall or cloudy sky.  

    Look through the scope at the reticle for only a couple of  seconds. Only long enough to see if the reticle is sharp. If not, turn the ring out just a little. Now look away. Close your eyes for a few seconds. Let your vision recover.

    Repeat. 

    This is the common method of getting the adjustable ocular set and is a starting point but I have been doing something different based on advice given in a blog post by the Crosman pro shooters. They recommend that it is more important to have the minimum amount of parallax through a scope in relation to any given person's eye than to have an arbitrary sharpness of the reticle. Your eye will quickly tend to focus on the reticle throughout a wide range of ocular adjustments. Hence the "only for a couple seconds" that is often recommended. But the adjustment of the ocular can serve for fine tuning other aspects of a scope also. Particularly noticeable at high magnifications of 25x and above.

    Here are my tips:

    Bench rest the rifle on a solid bench and bags.

    Dial in the highest magnification you want.

    Focus the side wheel on a midrange target that is close and complex enough to see differences in focus from the adjustments.

    Now bob your head in the exit pupil of the scope image while adjusting the side wheel focus. Try to find the focus setting that has the minimum parallax. Any parallax will make the image of the target move around under the cross hairs opposite from the movement of your eye even though the target and the rifle are not moving.  It can easily look sharp but still have +- half a mil of parallax for any given scope. Use the focus wheel to adjust for the minimum parallax while bobbing your head. The image of the target will appear to begin "rotating" around the axis of the cross hairs during extreme eye displacement with the bullseye still locked to the center when parallax is minimum, rather than seeing the apparent impact point move up and down and left or right on the target.  Which will not necessarily be at the setting of the sharpest focus.  

    Then adjust the ocular toward getting the best compromise between image focus and reticle focus. Which may shift the best parallax slightly. Adjust for best parallax again and repeat. You may also find that compromising the cross hairs slightly this way will result in a  sharper HD image down range than was available before even though both scenarios were adjusted for image focus as best as they could be. Tree bark is a good example.

    The sharpness of the illuminated reticle versus the black is another concern where all of these considerations can be compromised with the adjustable ocular to get the least fuzziness and shift of the red in relation to the black during head bobbing.

    I also tend to set the eye relief of the scope mounting slightly toward the too far range of the exit pupil ball which gives a slight dark ring around the image  but shows that when this ring is centered, that your eye is precisely down the center of the scope.

    I read a great tip for minimizing misalignment of the scope and rings which don't center it absolutely over the bore. 

    Set the rifle up on a bench again and sight at a mirror. 

    Simply rotate the scope until the cross hairs perfectly intersect the center of the bore.

    Any level indicator should then be on the scope tube when the cross hairs are true to a plumb bob . Not the breech. It doesn't matter if the breech is level. Only that the cross hair is true to the bore and that the cross hair is level when on target.

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    https://www.airgunnation.com/topic/scope-setup-and-adjusting-the-ocular/

     

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    Nathan
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    I get what you’re saying, ILya further explains here:

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