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Lens Refraction

Discussion in 'Shooting Related Threads' started by ismah, Jul 18, 2011.

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  1. ismah

    ismah Member

    Joined:
    Feb 19, 2008
    Messages:
    518
    Today while lining up the beads on my shotgun I took off my bifocals to check out what the site picture was. It was pointed left of where it was with the glasses on. I steadied the barrel against a door frame, sighted down the barrel, formed a figure eight and took off my glasses again. It was aiming left. I did this many times and concluded my glasses were bending my sight picture. What gives?! I've noticed over the years I tend to shoot left of targets. I compensate by aiming right of them. Is there a remedy? Suggestions will be greatly appreciated.
     
  2. dead on 4

    dead on 4 Well-Known Member

    Joined:
    Aug 4, 2009
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    3,070
    close your off eye and see what happenss

    surfer
     
  3. Ted K.

    Ted K. Member

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    Location:
    Tiburon, CA
    There is a possibility that the lenses in your glasses are not properly positioned.

    What I'm referring to is not where the glasses sit on your nose, but whether the lenses were ground so that, when you look through them at the beads on your shotgun, you are using the portion of the glasses which are intended for maximum visual acuity. (Acuity falls off as you move away from the center of the prescription. It's why the optometrist measures your pupil distance - to be sure that the center of the prescription is properly positioned in front of each eye.)

    The glasses you wear every day are set up so that your pupil is directly behind the center of the curvature that represents your vision prescription. But when you use everyday glasses for shooting, you move your chin down to contact the comb, causing you to look though the upper part of the lens (and possibly one side of the lens) in order to see the beads. If you are using your regular glasses, you will be looking through a part of the lens that is not really intended to be used for anything other than peripheral vision.

    Try this: get a magic marker and have a friend put a mark on the lens in front of your dominant eye (with your guidance) that covers the beads when you have the gun mounted. Then take your glasses to an optometrist and have them check to see if your prescription is centered around that mark.

    Or dismount the gun after making the mark and try looking through your glasses with your head positioned so that the mark is in the center of your gaze. Do objects move around or get fuzzy as you move your head? If so, you have found the source of your problem, and you need to get new lenses that put the center of the prescription right in front of your pupil when you have the gun mounted.

    Ted K.
     
  4. ismah

    ismah Member

    Joined:
    Feb 19, 2008
    Messages:
    518
    I think you nailed it Ted. I did as you suggested and it looks like need to get some new glasses. Objects move around when I move my head. I played with it again last night and the difference is worse than I first discovered. Thanks for the advice.
     
  5. Ted K.

    Ted K. Member

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    Location:
    Tiburon, CA
    Ismah -

    You have three choices:

    1. Take your shotgun to the optometrist, tell him this is NOT a holdup, and get him to figure out where the center of your prescription should be located when you look through your shooting glasses with the gun mounted. This approach can induce a lot of anxiety in the optometrist, particularly when you point the gun at him.

    2. Invite the optometrist to your trap club, where you can go through the measurement process described above. The problem here is that he thinks he has better things to do (he's wrong) and he may think you're nuts (he could be right or wrong on this one, I don't know).

    3. Get a friend to put a dot (using a felt tip pen, magic marker, etc.) on your glasses to mark the place where you look through the lens to see the beads. Basically, you want the mark to cover the beads. Then take the marked-up glasses to the optometrist and let him work from there to be sure the center of the prescription is in the right place.

    Ted K.
     
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