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Side focus question?

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: March/26/2008 at 14:57
mnhunter2 View Drop Down
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 On a Monarch 3-12x42 I was wondering about the side focus feature compared to a focus that is on the objective end, how often would you be using it and does the side focus turret cause any handling problems?
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: March/26/2008 at 15:32
supertool73 View Drop Down
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Superstool

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That side adjustment is actually parallax adjustment not a focus knob.  The one of the eye piece actually focuses for you.  Here is a definition of parallax

Parallax
Parallax is essentially an optical illusion.  Parallax presents itself as the apparent movement of the reticle, in relation to the target, when your eye moves off center of the sight picture (exit pupil) or in more extreme cases it appears as an out of focus image. It indicates that the scope is either out of focus or more specifically the image of the target is not occurring on the same focal plane as the reticle. Maximum parallax occurs when your eye is at the very edge of the sight picture (exit pupil). Even when parallax is adjusted for a designated distance, there is an inadvertent error at other distances.  Most brands of scopes that do not have a parallax adjustment are pre-set at the factory to be parallax free at or around 100 yards; rim fire and shotgun scopes are set at or around 50 yards.  Most scopes of 11x or more have a parallax adjustment because parallax worsens at higher magnifications.  Generally speaking parallax adjustment is not required for hunting situations and is primarily a feature used and desired by target shooters.  A 4x hunting scope focused for 150 yards has a maximum error of only 8/10ths of an inch at 500 yards.  At short distances, the parallax effect does not affect accuracy. Using the same 4x scope at 100 yards, the maximum error is less than 2/10ths of an inch. It is also good to remember that, as long you are sighting straight through the middle of the scope, or close to it, parallax will have virtually no effect on accuracy in a hunting situation.

 


Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: March/28/2008 at 09:28
mnhunter2 View Drop Down
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 So is I understand your answer correctly in general  hunting situation you would rarely use the side focus feature, more important for target shooting. 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: March/28/2008 at 09:45
Tip69 View Drop Down
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That is how I understand it....... not a big deal for hunting!  The only time it could be an issue for hunting might be with a .17HMR and a high powered scope, which is something you might use up close on small game (like 10 yards) and also at long distances for P. Dogs or target shooting (like 250 yds), then a side focus/AO would be important.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: March/28/2008 at 09:55
supertool73 View Drop Down
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Typically scopes that are under 12x on the max end do not have a parallax adjustment.  So you are right, most hunting scopes do not have and have no need for them.  Unless like Tip said it is a long range varmint rig or something like that.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: March/28/2008 at 10:05
8shots View Drop Down
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All the above are correct, except in my understanding is that parallax error is greater at shorter distances. The closer the target, the more likely you are to not alighn your eye with the center of the scope and thus create a parallax error. The further out your target is, the more likely you will center your eye. It is for this reason that all air-rifle competitors (who shoot at very short distances use parallax. This would also be why the higher the magnification, the greater the parallax error. You are in fact bringing the target closer to you. 
The side adjustment is handier or easier accesable to adjust whilst looking at the target. In target shooting one will readjust parallax every time the distance changes. The same for hunting. This is why parallax is not really a future in hunting scopes. It is set to 100m. Beyond 100m an error is less likely to occur, closer then 100m the error on a 10x scope on bullet POI is neglible.


Edited by 8shots - March/28/2008 at 10:12
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