Rifle Scopes POI shift when I change magnification???

[ScottyD]

I'm curious if any of you guys have seen this before and may be able to explain what's happening. I've got a SWFA 5-20x. Its been a great scope so far -I'm very happy with the glass, and the tracking has been great. I usually shoot up at 20x. I recently noticed that when I turn it down to 10x or 15x, my POI drops. I did a dot drill at 100yds: @ 20x: POI dead center, @ 15x POI 1/2" low. I repeated this test with the same result 3 times. I also did this test at 300yds on steel. @ 20x: dead center, @ 10x: POI was 2 or 3 inches low... Bummer. I assume this shift will get worse and worse the longer the distance. I'll be sticking with 20x! Any idea what might be causing this?

 

[Rob01]

Scott that's not right and you shouldn't have to shoot your rifle on 20x. This isn't the 1970s. Get a hold of SWFA customer service and see if they will help you out.

 

[ZombieSlayer]

Are you readjusting your parallax after changing magnification? If your not that could do it. If that's all it is at least you know you've got good consistent form.

 

[ScottyD]

I've been wondering if it might have something to do with parallax, or possibly how I've got my rear ocular adjusted? I've noticed with some scopes that your eye relief will change when you shift magnification. I haven't played with the parallax setting after turning the magnification down, but if you've got a good parallax setting at 20x, I'm curious, why would that change when you go to 10x? I may give swfa a call and see what they have to say as Rob suggested. Thanks....

 

[TheGerman]

Are you readjusting your parallax after changing magnification? If your not that could do it. If that's all it is at least you know you've got good consistent form.

This.

Can be a combination of parallax and you resting your head/face in a slightly different position due to the shrinking/growing eyebox when reducing/increasing magnification.

 

[Captain Kirk]

I agree with Rob, not right at all, something is wrong

 

[Dave@USO]

If you do not have your parallax adjusted correctly you can get a POI shift... As for setting up the ocular lens, this is a set and forget item.

Adjust the ocular one time and then leave it alone... Unless your eye sight changes.

I would call SWFA but only after testing some more things. correctly set your ocular lens then adjust your parallax for your power setting at your distance.

If you still get a POI shift then you will be able to tell them you have tested all of the steps needed.

Hope this helps.

 

[Kevin1]

I thought you need to go very high end (I’m talking $3000 S&B) for variable power scopes with no (almost) POI change when modifying magnification.
Isn’t a 1moa POI shift expected from a $1000-$1500 scope when changing magnification?

 

[stranded]

Kevin1, POI shift of that magnitude isn't something I have encountered the since seventies. (Tasco didn't even do that any more) I suspect bad paralax adjust or Bad scope as already mentioned. I did have a loose occular on a cheaper scope in this century, that was fixed by the factory warrenty. (Leupold rifleman 3X9)

 

[Temp9]

My $100 Vortex Crossfire didn't have any POI shift with magnification. Not normal at all. However, I thought FFP scopes couldn't have magnification-POI shift due to the design of a FFP. Can someone who actually knows something about optics confirm or deny this? I may just be remembering wrong.

 

[ScottyD]

Thanks for the help. Sounds like my next step is to try and see if I can eliminate the problem with parallax adjustment.

 

[Greg Langelius *]

Typically, magnification changes result in Exit Pupil size and Eye Relief alterations, which can in turn force the shooter to subtly alter their eye alignment/cheekweld in order to obtain a clear image. Any time the cheekweld alters (and is perhaps complicated by a parallax compensation discrepancy) so can POI. If the Objective lens is refocused, this will also often result in altered parallax compensation since many modern scope designs (perhaps incorrectly) couple the objective focus and parallax adjustment, which are in fact two different, though somewhat related, adjustments.