 AstroClassifieds.com |
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For Sale By
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Views
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Date Posted
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John Duchek
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457
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Sun January 13, 2008
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Asking Price
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Condition
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Distance from you
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$5.00
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New
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supersize
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Description:
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Maximizing the aperture of your telescope requires that you consider your personal optical equipment!
Pupil Size Gauge
When you are choosing the eyepieces to use with your telescope, do you take your eyes into account? Many folks don't realize that the maximum size of your eye pupil is what determines what your optimum low power eyepiece should be. By using a lower power eyepiece than the optimum, one effectively shrinks the aperture of the scope. Since pupils tend not to open as widely as we get older, it is clear that one needs to adjust to get the maximum performance out of our equipment (personal and purchased).
You can search the net and find many references on the importance of pupil size in determining your optimum low power eyepiece, here are two good ones:
Sky & Telescope, "A Pupil Primer"
When does your 8" telescope deliver less light than a 3"?
(see my website for these links)
The second one gives an indication of how important paying attention to this can be!
It also has a nice chart of pupil size vs scope speed (F/?) if you don't like the math.
I have a 14" F/4.7 and reasonably good eyes for my age (59). My exit pupils measure about 4.5-5.0. I find that my best, ie brightest images come with a 23-24mm eyepiece with that telescope(both by calculation and experience). Even if I had 7.0 mm pupils (about the best the normal young person could expect), ~ 32 mm would be the maximum for this scope. To use the 30-50mm eyepieces effectively one needs an F/10 or higher scope.
Also, since I relearning to program computers, I have put a free program on the download page that will calculate the match between your maximum pupil size and over 200 eyepieces. It will also estimate how much light will be lost if any in the combination of its exit pupil in your telescope and your eye. It also calculates their FOV while its at it. I will send you a copy (Windows and/or Linux format) on request.
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Keywords:
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Pupil Testing Gauge FOV exit entrance pupil size
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