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POI change with magnification change?

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Category: Scopes
Forum Name: Rifle Scopes
Forum Description: Centerfire long gun scopes
URL: http://www.opticstalk.com/forum_posts.asp?TID=8002
Printed Date: October/21/2017 at 00:00


Topic: POI change with magnification change?
Posted By: f1gpstar
Subject: POI change with magnification change?
Date Posted: October/02/2007 at 22:29
I have a simmons 6 x 24 w/AO and the POI changes when I change the Magnification?  Am I not adjusting the AO properly or is it the scope?

Thanks,

Bill



Replies:
Posted By: koshkin
Date Posted: October/03/2007 at 00:15
It is likely to be the scope.  A lot of inexpensive scopes have this problem.

ILya


Posted By: www.technika.nu
Date Posted: October/03/2007 at 02:13

Quite a lot of more expensive scope does also have this problem.

A test a saw some years ago proved that Leupold had the problems quite often.

 

Easyest way to not have POI problems is to have a first plane reticle.

 

Regards Technika



Posted By: Dale Clifford
Date Posted: October/03/2007 at 08:37

the poi change in SFP can occur several different ways. a quote from nightforce "decreasing magnification from specified settings will increase values of the ranging scale and bullet drop scale. increasing mag. will have the opposite effect and increase values". the important thing is it consistent such that this physical property can be used to easily recalibrate the SFP to ranging reticles to any magnification value. on higher power scopes such as yours, one can observe walking the bullet thru the target by changing the mag. power from high to low. this occurance is amplified when the bullet arc or trajectory has started a large part of its drop.  "as a varmit in .223 at 500 yds for example".

the second type of poi change occurs when the erector set is not "aligning" the image the same way each time. this is a scope problem regardless if the scope is second or first plane, in my opinion this is a problem zeiss has with some of their earlier ffp and causes an "tire" effect or tunneling, and while not considered a problem by them, drives me up the F%$#^ wall. while not talked about much horizontall poi changes are much worse,  even if consistent they are hard to work with in conjunction with verical, and are usually a result of a scope problem, either in design or execution.

poi changes cannot be "measured" with the usuall shooting box text, but using either a bore sighter or a gridded target at distance say 200 yards, one can count the clicks between at different powers. this test should be done by any serious shooter on a serious purpose scope and is the best way to check for tracking errors.

 even zeiss's 24 by 56' will do this because of its sfp



Posted By: www.technika.nu
Date Posted: October/03/2007 at 16:06

I completely agree.

All factorys have mondays, some have more mondays than others.

Usally is there fewer mondays the more  you pay for it....

 

Regards Technika



Posted By: Dolphin
Date Posted: October/04/2007 at 16:29
A laser bore sighter, those inserted into the chamber, is a handy device to check for poi with magnification changes and if any, measuring the difference, as well as the reproducibility.  Good devices can work up to 25 to 50 yards in the proper, lack of light and used with a gridded target can be useful to account for differences when hunting, especially if they are large.  Depending on where I am hunting, I rarely change my magnification from the power I used to sight in my scope, which was pre-determined by where and what type of hunting I was going to do.  Eliminates those problems.  Also, the problem, if occurs is obviously worse, the greater the magnification factor.  Dale's assessment is quite accurate and complete.  Therefore, this applies to scopes that do not have an erector problem. 

-------------
D. Overton



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