Exit pupil diameter is given by diameter of the objective lens divided
by magnification. The pupil diameter of the human eye varies from about
3mm in sunlight to about 7mm for the fully dark adapted eye. 7mm holds
for younger folks. We old farts might not have such a large pupil any more.
Whenever the exit pupil of the scope or binoculars is larger than the
pupil diameter the full light gathering ability of the objective lens is
not being utilized. That's because the beam of light can't fit into our
eye since the exit pupil diameter is greater than the pupil diameter.
The lesson is to not choose something large and heavy like 7x50
binoculars if your usage is going to be in bright daylight. 7x50
binoculars are called "night glasses" since they produce a 50/7 = 7mm
exit pupil. But if you're using them in bright daylight your pupil
diameter is only 3mm. You can get a 3mm exit pupil from a 7x21
binocular which in much smaller and lighter and the image will be just
as bright.
Your Leupold 2-7x scope has a 33mm objective. The exit pupil ranges
from 16.5mm to 4.7mm. You will probably find that maximum image
brightness well before sunrise will be about 5x. Going to lower
magnification will increase the angle of view but not the image brightness.
Chuck Norcutt
On 11/9/2015 8:32 AM, Dean Hansen wrote:
Moose posted: "It's a zoom scope, dood. 3 mm exit pupil @ 9x."
I have no idea what the exit pupil is on my Leupold 2-7 scope on my
Sturm-Ruger M77 .270. Nor, actually, do I care. Just know that we're both
counting down the days 'til Nov. 21, when we'll be seated in the deer stand
well before sunrise. Just us and nine antlerless permits.
Quantity Deer Management Dean
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