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Odd scope question

Discussion in 'Rifle Country' started by kestak, Jul 13, 2009.

  1. kestak

    kestak Well-Known Member


    I have an odd question about scopes. I have two 3-9x30 scopes.
    When it is at 3x I do not have to work hard to allign my head and I can be at various distance to have a clear picture. When the scope is at 9x, alligment is critical. If I am not alligned exactly right and at the right distance, I see black or most of the reticle is black. I think you know what I mean... :righton:

    If I buy a scope 3-9x50 for example, will the allignment and distance be less critical? Or is it all dependent of the scope?

    I know about eye relief. I have a Bushnell with long eye relief and it is worse than my shortest eye relief. With the long eye relief, I can't be too close or too far. I have also a target long eye relief and I can be close or far and position is less critical than the expensive Target.

    I am talking about scopes because I woudl like to put a high power scope on my varminter like

    Thank you
  2. Jim Watson

    Jim Watson Well-Known Member

    Exit pupil is calculated by dividing the objective lens diameter by the magnification.

    Set your 3-9x30 on 3 power and you just have to get behind a 10mm opening. But you have to line your head up behind a 3.3 mm image on 9 power.

    Go to a 50mm objective lens and the 9 power exit pupil becomes 5.5mm, easier to find.

    There are more complicated calculations done by the optics people to establish the "eyebox" that you can see through the scope from, but exit pupil is a good start.
  3. kestak

    kestak Well-Known Member


    Jim: So, the "eyebox" problem that I see will be less proeminent with a 40mm or 50mm. right?

    Thank you
  4. rcmodel

    rcmodel Member in memoriam

    Jim is exactly right.

    As he said, divide the the objective lens diameter by the magnification.
    That gives you the diameter of the exit pupil, or spot you can look through clearly.

    It is only a rough guide to the maximum size it could theoretically be, because all scopes are not created equal.

    Still, there is no denying it will be bigger & more forgiving on a 3-9x40mm or 3-9x50mm scope then on your little 3-9x30mm scope.

    Read this for a better understanding of it.

  5. lipadj46

    lipadj46 Well-Known Member

    Plus with most scopes you lose eye relief as you increase magnification so you need to move your head forward to get a proper sight picture.
  6. jmr40

    jmr40 Well-Known Member

    I'm not 100% sold on the idea that a 50mm lense will improve the ability to focus quickly. If it does at all it is less important than the particular scope in my opinion. I've got scopes with 32,36, and 40mm objectives and the Leupolds with 32 and 36mm objectives are easier to align than my Zeiss 40mm scopes. The Zeiss work better in low light than even the 40mm Leupolds.

    Dividing the objective size by the scopes power will give you a pretty good idea how much light will be able to get through in low light, but even that is dependent on the individual scope and the quality of the glass. A good quality scope with a 32mm objective will outperform most of the cheap 50mm scopes.

    In my opinion the eye relief is a much more important in being able to quickly align your scope. The 1.5-4X scopes with 20mm objectives are some of the fastest scopes to get on target.
  7. Walkalong

    Walkalong Moderator

    The 2.5-8X32 Leupold Vari X III has a huge field of view at 2.5, a good one at 8, and is easy to line up quickly at both ends of its power spectrum. It outperforms cheap 40 and 44MM objective scopes in clarity and the ability to see in low light. I have never had a 50MM to compare.

    Spending more money buying better glass is preferable to buying a bigger objective IMHO. Technically the 50 gives you more wiggle room, but different designs vary quite a bit as well. Find a quality scope that gives you the "alignment" qualities you are looking for.
  8. lipadj46

    lipadj46 Well-Known Member

    Eye relief is usually a better indicator in my experience. You will spend less time trying to get your head into the proper position if the scope has a generous amount of relief.

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