| Posted: Tue Jun 6th, 2006 06:54 PM |
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TwoBeards
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Ok all Im about to reveal a little bit of my intelligence here I purchased a Simmons 6x24x50 scope with AO for my 270 wsm now what is the purpose for the ao? Is it to eliminate parralax? This is my first venture with a high power scope so Im kinda lost here. Any help would be greatly appreciated. Jimmy
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| Posted: Tue Jun 6th, 2006 08:10 PM |
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drinks
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Yes, adjust for the distance, as a practical matter, either for close stuff, under 75 yds, or distant stuff, 125 yd on out.
Really not much use for average hunting purposes, is more of a target shooter thing.
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| Posted: Wed Jun 7th, 2006 03:21 AM |
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TwoBeards
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drinks wrote:
Yes, adjust for the distance, as a practical matter, either for close stuff, under 75 yds, or distant stuff, 125 yd on out.
Really not much use for average hunting purposes, is more of a target shooter thing.
Thank you very much, I wasnt sure so thought Id ask and I do appreciate your help Jimmy
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| Posted: Wed Jun 7th, 2006 04:43 AM |
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Texasdoc
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Ok here is waht Parallax is
Optics Tech > Parallax Explained
Whenever rifle scopes are discussed, a topic that frequently arises is parallax. There seems to be a great amount of misunderstanding and confusion concerning this subject. Parallax can be defined appropriately to rifle scopes as; the apparent movement of objects within the field of view in relation to the reticle.
In a telescopic sight, parallax occurs when the “primary image” of the object is formed either in front of, or behind the reticle. If the eye is moved from the optical axis of the scope, this also creates parallax. If the primary image is formed on the same focal plane as the reticle, or if the eye is positioned in the optical axis of the scope, then there is no parallax, regardless of the position of the primary image.
High magnification scopes, or scopes for long range shooting, where even slight sighting errors would be serious, should be equipped with a parallax adjustment. This adjustment of the objective part of the optical system would ensure that the target can be brought in the exact focal plane of the reticle at any distance. Tactical style scopes are not usually supplied with parallax adjustment because the exact range of the target can never be anticipated. Scopes of lower magnification are not usually supplied with parallax adjustment either, because at lower powers the amount of parallax is so small as to have no importance for practical, fast target acquisition.
THERE ARE TWO FACTORS WHICH CAUSE AND DETERMINE THE AMOUNT OF PARALLAX IN A RIFLESCOPE:They are;
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. 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 in which there is no parallax. In most rifle scopes this one point of no 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.
You can check the parallax of any scope by sighting an object at normal shooting distance (not indoors), by moving your eye side to side (or up and down), as far as you can, keeping the sighted object within the field of view. The apparent movement of the reticle in relation the target is parallax.
Rifle Scope Adjustment
The most misunderstood and often incorrectly set rifle scope adjustment of all .... is the parallax setting. This is NOT a focus adjustment or a range finder. This adjustment allows your scope to adjust the optics, so that the crosshairs will be correctly positioned when shooting at different distances. This is accomplished by adjusting the front lens to remove the parallax, making sure the image focuses on the same plane as the crosshairs . . . . not in front or behind them.
 The way to set this adjustment is seldom to just dial the correct distance printed on the scope. This adjustment usually needs to be set more accurately (with the rifle securely positioned on a bench) so that you can look through the scope. Then, while shifting your eye to the left and right, you can see if the crosshairs appear to move across your target. The purpose of the parallax adjustment is to eliminate this unwanted optical error that makes your crosshairs appear to "move".
Most scopes have a fixed parallax setting that is exactly correct for shooting at only "one" specific distance. If your scope has a parallax adjustment it can be perfectly adjusted for shooting at any distance, so that your crosshairs will appear to be rock solid, no matter where your eye is positioned. The crosshairs should appear stationary, as if they were painted on your target. This is very important when the "exact" position of your eye is not always concentric with your scope. The slightest variance can make a huge difference.
Very few parallax adjustable scopes will be set correctly if you just dial the yardage settings printed on the scope. This may sound incredibly basic to some shooters, but there are a LOT of good shooters out there that could cut their groups by almost 30% if they just knew how to make this scope adjustment properly. If you look around, I guarantee that you'll find shooters with great equipment, that have never gleaned this information from some of the poorly written instructions supplied by scope manufacturers.
It's a very good idea to re-label the parallax yardage markings on your scope, so that they are positioned correctly. Some shooters write yardage markings on a piece of white tape and position it on their scope, so that they will be properly located. Others will paint a few dots on their scope representing 50 yard increments - exactly where they should be for each distance. Keep in mind that even if you re-label your scope markings, you may still need to make very slight parallax adjustments to compensate for light, temperature, and humidity changes throughout the day - especially at long range.
Doc
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| Posted: Wed Jun 7th, 2006 10:02 PM |
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TwoBeards
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Excellent post Doc Thanks so much! I took the liberty to mark this topic important as your post should be kept up top as its very valuable information. Again Doc thanks!!! Jimmy
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| Posted: Mon Jul 23rd, 2007 03:31 AM |
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sako06
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I had an Adjustible Objective Scope on my 06 Browning Semi Auto, big mistake a Blacktail Buck was sort of in my sights until I looked thru the scope at a very blurred image of the buck fired and missed just at sunset.Returned home and bought a Weaver K6 .I then bought a used 06 Sako Finnbear with a Redfield Accutrack Scope which I sold and replaced it with a Leupold 3x9x40 with a CPC reticle which became my favorite . Last edited on Mon Jul 23rd, 2007 03:32 AM by sako06
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| Posted: Sun Nov 8th, 2009 01:36 AM |
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TnTom
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thanks TexasDoc its what I've waited a long time to read.
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| Posted: Fri Nov 13th, 2009 09:05 PM |
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-6
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Real good explanation--appreciate it, wc
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| Posted: Sat Nov 14th, 2009 11:34 PM |
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OldStuffer
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Excelent information.
I have a 4.5x14x43?(if I remember objective size right) Simmons Whitetail Classic, with A.O. on my .308 BAR, been there since arround 2000, been an excelent scope, am very happy with it, and now I know how to adjust it better.
Thanks from here too. :)
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