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Re: kahles advice 8x or 10x

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/11/2005 at 21:19
heatherbvann View Drop Down
Optics GrassHopper
Optics GrassHopper

Joined: August/11/2005
Status: Offline
Points: 1
I am trying to decide whether to purchase a pair of 8x42 or 10x42 kahles.  Can you tell me the advantage and disadvantage of each?  I know that the 10's magnify slightly better but it doesn't seem to be that big of a difference, and I was wondering if the 8's may do better at dawn and dusk.  However, I was confused when I saw that the 10's had a better twilight factor.  I will be using the for hunting whitetails in nc and will seldom be glassing deer at much over 250-400 yards.  Please let me know which you feel will be best for this. thanks.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/11/2005 at 21:54
gremlin View Drop Down
Optics Apprentice
Optics Apprentice

Joined: February/16/2004
Location: left of center
Status: Offline
Points: 115
The Kahles 8x42 are my primary hunting binocular.  The difference in a 5.4mm exit pupil and a 4.2mm exit pupil is going to be most noticeable at dawn and dusk.  The 8x42's are going to yield about 25-30% more lighted image to the pupil in your eye.  In bright sunlight, the pupil of your eye probably won't be much larger than 2-3 mm so the difference at noon would be pretty much irrelevant.

As the sun dims or before it brightens, your pupil will expand (depending upon your age and relative health) to anywhere from 5-7mm as it tries to draw in more light.  That's when the size of the exit pupil on your binoculars is going to matter most--if it's smaller than your pupil it's going to be harder to keep the image aligned with your eye and the overall image is not going to appear as bright.  It's a chemical property that's hard to defeat...

Once your eye is properly aligned, however, and IF you hold your binocular perfectly still, then the 10X power will start to overcome the affects of the smaller exit pupil.  The fact that you have the extra magnification means that your binocular will provide a larger image to your pupil of the individual subject at the center of your objective lens.  In addition, because the objective lenses in this example (42mm) are the same, the image in the center of the 10x binocular will resolve more detail.

Until you lose alignment between your eye and the exit pupil of the binocular.

At that point, the 8x42 gains the advantage again.  Firstly because it's less likely to lose alignment because the exit pupil is larger and secondly because it's easier to regain alignment for the same reason.  In addition, the 18mm eye relief of the 8x42's is 3mm greater than the 10x42's.  This comes into play when you try to determine how quickly you will be able to bring your eye in alignment. 

My experience has taught me that the greater the eye relief--in this case, the 8x42's have a 17% advantage--the faster your eye can begin resolving the image it's being shown.  That is a mighty important feature when I try to make a decision of whether or not it's time to set down my glasses and pick up my thirty-ought-six.

Most young hunters seem to prefer more magnification and go with 10X's.

This old hunter prefers the more generous exit pupil, broader field of view, and greater eye relief.  I leave the high powered magnifying to my Leupold VXIII riflescope.  I just need my binocular to pick out a target and the 8 power 42's allow me to do that faster and more reliably than 10 powers do.

In any event, they're both Kahles binoculars and neither one is gonna do you a disservice.  This is a choice between great and greater.

Just my two cents.
Take the long way home...

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/12/2005 at 15:03
ranburr View Drop Down
Optics Master
Optics Master

Joined: May/16/2004
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Points: 1082

I am at an in between age in life and I cannot tell a difference between the 8and 10X binos as far as brightness.  I could tell a difference in magnification.  I picked the 10s.  Some people have a problem with shakes with the 10X, if this is the case with you get the 8s.



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