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FoV and Exit Pupil question

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/12/2009 at 09:19
tpcollins View Drop Down
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I admit I am clueless when it comes to understanding a scope I guess. I'm now aware that objective size doesn't influence field of view - only allows more light to enter. But when I compare specs of a Swarovski 3-9x36 Z3 to the 3-10x42 Z3, the smaller 3-9x36 has a larger 39-13.5 FoV versus 12.6-11.7 on the 3-9x42.  The 3-9x36 seems to fit my needs if that's really correct. I understand how Exit Pupil is defined but not what it means. The 3-9x36 is listed at 11.9-4.1 and the 3-10x42 is 12.6-4.2, but on another forum someone said if your pupil dilates to 5mx, a scope with anything larger than that is wasted . . . . . what does that really mean?
 
Obviously my priorities are quality optics, FoV, and low light capability. I'm just concerned that the 36mm objective won't give me as much low light brightness.   Any help would be appreciated, thanks.
 
I just found this, which really supports my confusion!!!
 
Exit Pupil
The circular image or beam of light formed by the eyepiece of a telescope. To take full advantage of a scope's light-gathering capacity, the diameter of an eyepiece exit pupil should be no larger than the 7mm diameter of your eye's dark-adapted pupil, so that all of the light collected by the telescope enters your eye. (The eyepiece exit pupil diameter is found by dividing the eyepiece focal length by the telescope focal ratio.) Your eye's ability to dilate declines with increasing age (to a dark-adapted pupil of about 5mm by age 50 or so). For those in this age group, eyepieces with exit pupils larger than their eyes can dilate to simply waste their telescope's light-gathering capacity, as some of the scope's light will fall on their iris instead of entering their eye.


Edited by tpcollins - December/12/2009 at 09:23
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/12/2009 at 10:24
jonoMT View Drop Down
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First of all, looks like a typo there: The 3-10x42 FOV should read 33-11.77. It's not uncommon for scopes of the same/similar magnification and objective size to vary in FOV. With Swaro glass you can get away with the lower exit pupil of the 36mm objective (more than you can with a cheap scope) but the 3-10 still has a decent FOV @ 3X and better low-light performance and perhaps resolution because of the larger objective.

Depending on your age, your eyes might not be able to make use of the full exit pupil, but it doesn't hurt to have it. I also don't see any advantage in terms of weight or length to the 3-9 and the objective is not that much larger so ring height should be the same. Price might be the only consideration then.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/12/2009 at 10:25
billyburl2 View Drop Down
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Exit pupil on those two scope are so similar that IMHO, it doesn't really matter. 1/2mm on the high end, and .1mm on the low end are pretty close. Exit pupil, simply stated, is how big a hole the light really has  to make it through the scope.Sense these two scopes are really even in this regard, chose the one that you prefer.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/12/2009 at 10:47
tpcollins View Drop Down
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jonoMT -  you're right, 33-11.7. I've just have too much stuff written on my sheet of paper. I  think I understand but without being able to compare them side by side at dusk or dawn, it's still a tossup.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/12/2009 at 14:53
silver View Drop Down
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Coating matter more in todays world than exit pupil.  Its like comparing engines without looking at the compression ratio.  While things may look the same on paper, there is a differance between a 2 liter Kohler and a 2 liter Porsche.
 
The coatings are what you are paying the extra money for. They make and break optics. 
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