I read an article once about 50 or bigger objective scopes...seems they were saying that our eyes(rods cones) CANT use the light provided by larger scope objectives once they change over into our night vision mode.
I read that a long time ago and wish I knew where Id like to re read it.
But I wil tell you what I think of a 50 NXS tonight.
Optics usher light to your eye
The human eye is wonderfully designed to gather more, or less, light as conditions around you change. Even state-of-the-art optics can't compete with the ability of your eye's iris to control the pupil size, which acts much like a variable aperture for the retina. The aperture for a binocular, spotting scope or monocular is fixed and limits the amount of light gathered through an optical lens. This is why it's important that you select a model that provides the amount of light you need to view as conditions grow darker.
How your eye responds to light
The eye pupil can change in size from about 2mm in bright light to up to 8mm in low light. As you grow older, the ability of your eye pupil to dilate slowly decreases. For example, most eyes dilate to about 7mm or 8mm at age 20, but by the time you reach 50 your eyes may only dilate to around 5mm. Keep in mind that hereditary and environmental factors may also affect how much your eye dilates at various stages in life.
How the exit pupil affects viewing
The exit pupil is an indicator as to how well you will see an image on a bright day, at twilight or at night. Knowing the exit pupil can help you choose a binocular that is well-suited to the light conditions you are viewing in.
Exit Pupil = Objective Lens Diameter divided by Magnification
The exit pupil is the magnified image in the eyepiece as it leaves the binocular to enter your eye. You can actually see the exit pupil of a binocular, monocular or spotting scope as a circular beam of light when you look at the eyepiece from arm's length.
2mm to 3mm for viewing in bright light conditions.
4mm to 6mm for observing at most any time of the day.
6mm to 8mm for viewing in the darkest conditions.
When the exit pupil is smaller than the pupil of your eye, the amount of light falling on the retina will be less than what you could really use — and the image appears less clear and dimmer. When the exit pupil of the binocular is larger than the pupil of your eye, some of the light coming through the binocular will fall on the iris where it doesn't get used at all (follow the path of the 5mm exit pupil in the diagram above). However, if you find yourself boating a lot, you may find it easier to keep your eye centered in the larger 7.1mm exit pupil of a 7x50 binocular.
This is not the article I was refering to but covers it pretty well.
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Last edited by NYLES; 10-12-2007 at 08:53 AM.