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What makes a Scope Fussy on Eye Position

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/13/2006 at 18:16
macky View Drop Down
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What makes a scope more or less fussy about your eye position ... meaning that some scopes aren't as forgiving when you eye is off-center or too close or too far away and they show darker rings around the image or from side to side

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/13/2006 at 21:00
Chris Farris View Drop Down
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It is primarily caused by a small exit pupil.  High magnification in relation to a small objective lens = small exit pupil.

 

Read more about exit pupil here.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/13/2006 at 22:42
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What he said- but adding- the relationship between the cheek weld and the "sight path" if the comb is off, causes fuzzies. it will not allow the eye to be in line with center axis of the scope. Long range prone target shooters prefer to behind the gun and is a hard positon on the neck, thus they like risers on the comb. Varmit hunters usually across a pick-up or something else which allows an angle and less rise in the comb and more cast off. A quick shot in heavy timber might see a straight stock with no comb. It helps to have the best of both worlds, good scope good stock.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/14/2006 at 03:06
macky View Drop Down
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I found a post that says to go for between 5 and 7 for exit pupil.  And divide Objective size / Magnification to find the exit pupil.  So I guess that's saying if I have a 50mm Objective, a magnification of 10x puts me at a 5mm exit pupil.  So are there other factors that come into play for exit pupil on High Power Scopes?  Say you have a 32X Scope ..... I think that would mean we would need an objective between 160 and 224 to be between the 5 and 7 exit pupil.  Using a possible scenario (32X with a 50mm objective) we have a 1.56mm exit pupil.

 

As far as eye position is concerned .... let's use the case where I am target shooting.  I'm taking my time and getting lined up ... but what makes the precise location of my eye more critical?

 

Is that just the nature of the beast?  Meaning when we get into higher magnification, and we are limited by exit objective size (like maybe 50mm) is the eye position just going to have to be more precise.  So what we do is go for the largest objective that we can to help reduce how precise that position really is?      

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/14/2006 at 04:26
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Originally posted by macky macky wrote:

What makes a scope more or less fussy about your eye position ... meaning that some scopes aren't as forgiving when you eye is off-center or too close or too far away and they show darker rings around the image or from side to side

 

The lens in the scope have to focus the light down to a point.  Let me try an asci visual, >-- 

As you move away from that point you see less.  A higher quality product may be slightly more forgiving as the image quality is better at the edges.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/14/2006 at 05:47
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I found a great piece for reading.  It's in "The Gun Digest Book of Sporting Optics" written by Wayne van Zwoll.  ISBN: 0-87349-322-2.  Starts on page 115 ... section is titled "Understanding Scopes".  It covers Parallax, Eye Relief, Exit Pupil, FOV, Magnification, Glass Quality the inter-relationship of them all .... and MORE, MORE, MORE.  The section itself is 8 pages.  It is the most clearly explained piece of reading that I've read about the subject.  IMHO definitely worth reading.

 

Kinda boils down to like Chris said .... key factor in making a scope more fussy when it comes to eye position is exit pupil .... add to that eye relief.  Seems that "eye relief of quality scopes" varies less as magnification changes.  This makes your forward/rear eye position more consistent at all magnification settings.  As far as the right/left or up/down fussyness is concerned .... the image is projected in the shape of a cone.  The wider the "exit pupil is" the wider the opening of the cone is .... if that cone is wider (your pupil doesn't sit at the vertex of the cone ... it's further forward) then the less fussy your scope is for up/down and right/left placement of your eye.

 

I hope I got that all right ....

 

So I guess if I'm looking to minimize how fussy a scope is for eye placement

 

1.  The better quality scopes will help on consistent "eye relief" no matter what magnfication (variable power)

2.  Bigger Objectives (and I guess tubes) will help on up/down and right/left placement.

 

 

 

 

 

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