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Parallax Adjustment

Discussion in 'General Firearm Discussion' started by sadiesassy, Jan 29, 2012.

  1. sadiesassy

    sadiesassy Prescott Active Member

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    Never had a scope with a adjustable Parallax Adjustment. In this case it is called a side focus parallax adjustment.
    Conceptually I think I understand Parallax.
    The factory setting is for 100 yds.
    But I am trying to understand how to use this.
    Probably need to go out to a range to play with it more

    Question 1: I sight in at 200 yds - does that mean I should dial it up to the 200 setting? Or keep it on 100 yds ( Factory setting)?

    Question 2: If I have it set on 100 yds and go to 200 yrds or 300 yrds - does that affect where the bullet impact is at vs lets say moving the adjustment to 200 or 300 yds. Think I am asking the right question - Does the distance to the target and the associated parallax adjustment affect POI. If adjustment is at 100 yds and I shoot at 200 yards - can I expect the impact to be off lets say 1 MOA more than if it was matched?

    Question 3: I read somewhere you can estimate distance with the parallax adjustment – they still recommend a range finder - But how do you estimate distance?

    Appreciate any input.
     
  2. madcratebuilder

    madcratebuilder Ardenwald, OR Well-Known Member

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  3. AnthonyL

    AnthonyL Tacoma, WA Member

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    The latest Magpul Dynamics video on Precision Rifle shooting had a great explanation of parallax adjustment.
     
  4. sadiesassy

    sadiesassy Prescott Active Member

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    Thanks fro the information on sites to visit
     
  5. doubletap007

    doubletap007 Beaverton Active Member

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    i dont use my parallax adjustments so not much help there but i think using your reticle as a rangefinder is what you mean?
    with your reticle the lower bar to the verticle line is 16" at 300 yards.(brisket to backbone on a deer is 16" at 300 yards.
    therefore if you have a target which measures 16" it should fit in that windage line to bottom of elevation line.
    if it's further than 300yds it will be too small to fit that area,too big wont fit that area(clear as muddy water?)sorry best i can do.
    I like varment reticles for this purpose,there are so many different ways to measure distance through them,not to mention if you can hit a squirl at 300 yards you can hit the squirl in the deers pocket at 300 yards to use an uncle ted analogy.
     
  6. sadiesassy

    sadiesassy Prescott Active Member

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    Thanks
    I saw something on that the other day.

    I got the impression that you can use the parallax adjustment to estimate the yardage.

    I will have to go out and play with it
     
  7. doubletap007

    doubletap007 Beaverton Active Member

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    TWO FACTORS WHICH CAUSE AND DETERMINE THE AMOUNT OF PARALLAX IN A RIFLESCOPE:

    1. The distance of the target to the objective--The objective lens forms a primary image of the subject being viewed and subsequent components invert the image, and there is no parallax. The actual position at which the image is formed is dependent on the distance the target is from the objective. Closer targets are formed farther away from the objective and farther targets are formed closer to the objective. Since the reticle is in a fixed position within the scope housing, the image is not always formed in the same plane as the reticle and, hence parallax.

    2. The distance the eye can move from the optical axis of the scope, is determined by exit pupil size. There is no parallax, at any distance, as long as the eye is lined up exactly with the optical axis of the scope. An exit pupil small enough to do this would be impractical. It is important to know that in every scope, there is some parallax. It is also important to know that in every scope, there is some one shooting distance at which there is no parallax. In most rifle scopes this one point of zero parallax is usually placed at a suitable mid-range point in the scopes' focal range.

    In lower-quality scopes, there are other sources of parallax. If the reticle is not precisely placed the correct distance from the objective, the distance of no parallax will be exaggerated. Reticles that are not securely mounted and allowed to move even a few thousandths of an inch, will always have changing amounts of parallax. Parallax is also caused by optical deficiencies in the objective, either by design or manufacture. If spherical or astigmatic aberrations have not been corrected, images will form a considerable distance from the reticle. If you see a scope in which the apparent movement of the reticle compared with the image viewed is different from when you move your eye up and down than when you mover your eye side to side, it is because of a bad objective. No adjustment of the scope will eliminate these faults or optical deficiencies.
     
  8. Otter

    Otter Oregon - mid Willamette Valley Active Member

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    Lots of explainations about what it is but here is how to use parallax adjustment on a scope.

    First, if the dial has number on it, disregard them. The 100 yard setting might be 100% parallax free at 100 yards, but unlikely. 100% parallax free will probably be on one side or other of that mark. I think only one of my 7 scopes with parallax adjustment that have numbers actually line up perfectly. My highest quality scopes just have hash marks and no numbers on the parallax adjustment dial.

    Next, position the gun in bags so that it is perfectly stationary. Line the reticle up on a very fine aiming point. Don't touch the gun, look though the scope, and move your head up and down and back and forth. If the reticle moves off the aiming point, you need to correct for parallax. Slowly adjust your dial or objective while doing the bob and weave behing the scope until you stop seeing the reticle move. When it no longer moves, you have correctly eliminated all the parallax. If the gun is not perfectly stationary, I doubt you will ever get it perfect....maybe close but not perfect.

    If you are at 100 yards, and your parallax adjustment dial lines up perfectly on 100 yards, you can kinda sorta estimate range with a scope that has parallax adjustment. If the numbers don't line up you can do a calculation to figure out how far off it is, but it won't be all that accurate. Frankly I can guesstimate range out to about 300 yards with my eyes about as good as I can with the technique you describe.