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Field of View -why aren't all 3 X 9's the same?

 
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Old 12-21-2006, 05:47 PM
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Field of View -why aren\'t all 3 X 9\'s the same?

I have a couple of Leupold 3X9 Var II's. The field of view when cranked all the way up to 9 is not nearly as 'close' as other scopes I've used (like some cheap Bushnells). Friends of mine have have Nikon Bukmaster 3 X 9's that also have a smaller field of view (object appears closer). It really hasn't bothered me until I started hunting my new stand this year. Shots are 200 yds - 300 yds. At 200 yds cranked to 9, it's not too bad. 300 yds is a stretch for the Leupold 3 X 9 Var II. I'm thinking of buying a new scope and was thinking of getting a 4 X 14 of some brand to replace the Leupold 3 X 9. Why is there a difference in the FOV and has anyone else experienced this with Leupold?
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Old 12-23-2006, 08:56 PM
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Re: Field of View -why aren\'t all 3 X 9\'s the same?

Scope manufactureers round off the magnification to the nearest whole unit. The Leup V2 3-9X magnification is actually = 3.3(3x) 8.6(9x). So if the Leupy is 8.6 and maybe a Bushnell is 9.2 at the top end there will be a little difference.
The field of view is the width of the area that you can see at 100 yards. It is related to the magnification and decreases with increasing magnification.
Leupy = FOV @ 100 yds (ft): 32.3 @ 3x ,14.0 @ 9x
Bushnell 36 @ 3x , 13 @ 9x
It also depends upon the exact lens system the manufacturer uses. The Bushnell has a smaller field of view than the Leupy and therefore a deer fills up the view more so than the Leupy. It may be that rather than there being any real difference in magnification, what you are really seeing is a small field of view in the Bushnell which makes the deer appeared to be more magnified than it really is.

At one point in time in my life I knew how to measure magnification and it involves useing two eyes and two rulers but I do not at the moment remember the details of how to do it.
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Old 12-24-2006, 04:23 AM
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Re: Field of View -why aren\'t all 3 X 9\'s the same?

Regardless of the actual power of the scope (which may vary a bit) the real culprit is the diameter of the eyepiece, and the eye relief.

Say that you have two scopes that are exactually 9x. They can have different field of views. This is because of the differences in the diameter of the eyepiece, and the distance to the eye (eye relief) of the scope.

The reasons are the following... think of the diameter of the eyepiece as a window that is looking at the scene. At a fixed distance, the larger the window, the more you see.

And... the closer to the window your eye is, the wider view you have.

This is why a 4x pistol scope has a field of view of ~9 feet, and a 4x rifle scope has a field of ~24 feet.

And... even amoung rifle scopes, a 9x with 3" of eye relief will have a larger field of view than a 9x with a 4.5" eye relief.

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Old 12-24-2006, 05:22 PM
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Re: Field of View -why aren\'t all 3 X 9\'s the same?

Thanks for the responses guys. I'm sure you're right, still not sure I understand, I'll need to think about this one.
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