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| 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. |
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Terms of Sale | PRIVACY POLICY 7/1/2004 | Fine Print
Toll-Free Telephone Astronomics: 800-422-7876; Christophers, Ltd.: 800-356-6603
Alternate Telephone: 405-364-0858 24 Hour Fax Line: 405-447-3337
Telephone Hours: Monday-Friday 8 AM - 9 PM CST
Saturday Noon - 5 PM CST
Store Hours: Monday-Friday 9 AM - 5 PM CST
Saturday Noon - 5 PM CST
Astronomics / Christophers, Ltd.
680 S.W. 24th Ave.
Norman, OK, 73069
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