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Fisheye effect on lower power

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hawk45 View Drop Down
Optics GrassHopper
Optics GrassHopper


Joined: October/25/2010
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Post Options Post Options   Thanks (0) Thanks(0)   Quote hawk45 Quote  Post ReplyReply Direct Link To This Post Topic: Fisheye effect on lower power
    Posted: October/08/2018 at 15:15
Hi all,

In the market for a new scope.  Been some time so wanted to get out and see in person how nice some of the scopes I commonly see recommended really looked mounted up and glassing.  Since it's been some time I wanted to see how advanced the glass of lesser priced scopes compared to some of the higher end and commonly recommended scopes/models.   

I was looking at variable ranges from 3/4 - 15/18 for the most part in hunting and more tactical models from $600 to $1300.  

A few of the higher end models surprised me that when on the low end power (3x or 4x) as I was moving the scope back and forth looking to the other end of the big box store I was getting a fisheye effect at the edges.  I've heard about this on 1x scopes, but not on higher powers.  Is this a defect of the optic or is it a scope setup issue that can usually be corrected by the user (dioptre?)?
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Nixterdemus View Drop Down
Optics GrassHopper
Optics GrassHopper


Joined: October/05/2011
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Nixterdemus Quote  Post ReplyReply Direct Link To This Post Posted: October/12/2018 at 11:51
That 'fisheye' effect might be the artifacts of Globe Effect commonly called Rolling Ball. This became prevalent w/intro of Swarovision bins. I have a $200 scope, 3.5-10X, that exhibits the same at lower powers, but around 8X it sorta disappears. It doesn't really go into a cloaked mode it's just that as the FOV narrows one does not notice the phenomenon w/same intensity. Or at least I do not. 

Plus, not everyone percieves Globe Effect. I saw a post on a scope as mine and the fella described the view as funhouse glass from inside a carnival sideshow. It doesn't bother me, yet I see it. You might note that perchance the FOV is wide compared to other scopes w/same variable power, objective size & focal length.

As always, YMMV ... 
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hawk45 View Drop Down
Optics GrassHopper
Optics GrassHopper


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Post Options Post Options   Thanks (0) Thanks(0)   Quote hawk45 Quote  Post ReplyReply Direct Link To This Post Posted: October/16/2018 at 12:11
Great response and thanks.  Yeah, I've never noticed before but now see it in a few scopes.  Maybe my eyes are changing.  Was not surprised to see on some lower end scopes (relative $300) but surprised on some $1000+ optics.  Again if it's just my eyes causing the effect, it's not the makers fault.  But weird that many different makers optics at the same low power and some show the effect and others don't.
Good information going forward.  
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Nixterdemus View Drop Down
Optics GrassHopper
Optics GrassHopper


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Post Options Post Options   Thanks (1) Thanks(1)   Quote Nixterdemus Quote  Post ReplyReply Direct Link To This Post Posted: October/16/2018 at 15:15
I merely offered one suggestion that potentially might be the explanation.

If you see globe effect/rolling ball/Swarovision it is because of your brain's interpretation and the lack, or very little, of pincushion distortion. The only reason pincushion distortion is introduced, as far as I know, is to counter the globe effect in individuals that notice.


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hawk45 View Drop Down
Optics GrassHopper
Optics GrassHopper


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Post Options Post Options   Thanks (0) Thanks(0)   Quote hawk45 Quote  Post ReplyReply Direct Link To This Post Posted: October/21/2018 at 08:13
Much appreciated.
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