John C. Polasek wrote:
On Mon, 4 Aug 2008 06:11:56 -0700 (PDT), wrote:
I have recently bought a pair of Nikon ATB Monarch 8x42 binoculars
mainly for outdoor use and wildlife observation.....
Is 8x42 really useless for night sky observation on can I see
some planets besides the Moon? ....
You may be interested to know that your eye, in night accommodation,
opens to 7 mm. The exit pupil or "light spot" from an 8x42 = 42/8 =
5mm. The exit pupilfrom a 10x70 is 70/10 = 7 mm. Any exit pupil
larger than 7 mm will be of no value.
The intensities are as 7^2/5^2 = 49/25 = 2:1.
For the mathematically challenged amongst us, was that a yes or no to
the query?
Are you saying a pair of 10x80's will be no good, and a pair of 7x30
will be better?
Thanks
Alan.
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