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patter1
professor emeritus
Reged: 01/19/05
Posts: 597
Loc: Canada
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Re: What does the 'Visibility Index' tell you?
01/03/07 06:20 PM
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Quote:
My targets are galaxies, nebula AND star clusters. So an emphasis on aperture?
Star clusters generally benefit from magnification, so emphasis on both, like for most people. For all-round use, you wouldn't want something that has very high magnification and very small aperture, or vice versa; For general useage, an exit pupil of around 5mm is a good compromise between aperture (size and weight) and magnification.
Quote:
The idea is to move on from my existing 15x70mm Skymasters (multi-coated, BAK-4) to 20x90mm Strathspeys (fully multi-coated with broadband coatings on all surfaces including the prisms, BAK-4)
20x90 is a very good all-round size, and you'll see quite a bit more than 15x70, but probably more due to the greater aperture and magnification than coating differences.
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Patrick
8" f/6 NewStar dobsonian
Orion Starblast 4.5" f/4 mini dobsonian
42mm SuperView, 17mm Nagler T4, some other cheapies
Omcon 7x50, Oberwerk 11x56, Olympus DPS-R 7x35, Olympus Magellan 8x25
homemade 50mm right-angle bino-scope prototype
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