Adjustable Objective necessary on Scope?

Discussion in '.22-Rimfire Forum' started by jjfawks, Nov 30, 2009.

  1. jjfawks

    jjfawks New Member

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    Nov 28, 2009
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    I am looking at getting a 3-9x scope probably on the 30mm objective. Is it important to get one with adjustable objective for parallex, or is this not really a problem in this magnification range?
  2. cakes

    cakes New Member

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    Northern Maine
    My personal opinion:

    Parallax adjustment is not needed. For regular hunting situations, you will never notice the difference. The only time I would suggest a scope with an adjustable objective is for a long distance target rifle or a "prairie dog rifle".
  3. raydcarter

    raydcarter New Member

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    I think that depends a lot on your intended use. I punch paper at various distances and do a lot of airgunning as well. IMHO - a decent AO scope does not cost much, so why not? On the other hand, with what I do, I'm usually working with higher power than that. With the shooting that I do, I would not seriously consider a non-AO scope. You'll find some decent AO scopes in the 3-12x or 4-16x range well under $100.
  4. LDBennett

    LDBennett Active Member

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    The Adjustable Objective is the "focus" of the scope, just like on a camera. Without it it is like a fixed focus camera which gives a compromise focus at distances other than the one distance it is focused at. For low power scopes your eyes compensate for lack of exact focus whereas in high power scopes the difference is too great and your eyes will notice that the image is out of focus. But there is more to it than just focus... there is parallax. Let me explain how scopes work.

    Scopes are telescopes with an additional optical system that erects the image (it would otherwise be upside down). There is also a lens system in the back of the scope (the ocular) that you view the telescope's image through. Scopes also have cross hairs. The image from the front lenses is suppose to focus on the plane where the cross hairs are positioned. The rear ocular elements adjust to focus for the eye on that cross hairs plane. But if the target is at some other distance than the one preset at the factory, the image forms in front of or behind the cross hairs. Your eye quickly shift back and forth between the two planes to keep all in focus unless that distance is too great for the eye to accommodate, in which case one or the other looks out of focus. This effect is greatest on high power scopes.

    If you do not center the image in the field of view then the cross hairs will not line up correctly and will not represent the place where the barrel is pointing. That is parallax. It is eliminated if the image is centered or the object lens is focused so that the image focus falls directly at the cross hairs.

    Low power hunting scopes (under 10 power) don't really need an adjustable objective if used for hunting or target shooting close to the preset focus, usually 150 yds. But you must center the image in the field of view or a small parallax error may effect the point of impact if the target distance is at some other distance. Scopes expressly labeled as 22 scopes are typically preset for focus at 50 yds.

    There is a class of scopes used for target shooting (usually 22 competition) that has adjustable objective focus all the way down to 10 meters (about 30 feet) and is often used for air guns or 50 feet 22 competition.

    Adjusting scopes for focus is often done wrong. The shooter should view the sky and not the target and focus the rear ocular lens to get the cross hairs as sharp as possible. Then the front objective lens should be adjusted to get the target as sharp as possible. Do it any other way and you may introduce parallax errors. Non-adjustable objective scopes should be focused with the rear ocular by pointing at the sky too, not on the target

    Most all my guns are for target or varmint shooting and have high power scopes with adjustable objectives. I prefer those but I certainly can see how a hunter would not need that feature at all. For plinking no adjustable objective scope is needed since rarely is the distance for plinking targets only one distance. But remember to keep the image centered in the field of view to minimize the effects of parallax.

    LDBennett
  5. fr3db3ar

    fr3db3ar New Member

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    Mar 31, 2009
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    I'll call it personal preference. I like AO and have it on all of my scopes except for my 4X s. I like to shoot some long distance and I'd call it a requirement for that. When squirrel hunting with a variable and AO I just set the AO to about 35 yards and don't mess with it during the hunt.

    I hate shooting at a blurry target.
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