RE: [Utah-astronomy] f/4 or f/5? Why not try...
If I decide to upgrade, I'll think I'll go with the f/5 version. There is less of a central obstruction with the f/5 than the f/4.5. An f/4 has too much coma and is harder to collimate. The image size is a little bigger with the f/5 version. And the Paracorr is not necessary. For Dave Kriege, the f/5 is a "no brainer". I'm thinking about purchasing a trailer first before upgrading. I want to be able to view with my refractor and my reflector plus have room for sleeping bags and such. The Kolob Reservoir site is about an hour and twenty minutes from my house so I think it is wiser to sleep up there until morning. Debbie ps missed you up at Wolf Creek Pass. It was very cool and confortable up there. I may just head up there next month
[Original Message] From: David L Bennett <dlbennett@mac.com> To: <utah-astronomy@mailman.xmission.com>; Association Utah <uvaa@mailman.xmission.com> Date: 8/30/2004 10:08:30 AM Subject: [Utah-astronomy] f/4 or f/5? Why not try...
Why not go for a 16" f/16.5? See the mirror being offered at:
http://cgi.ebay.com/ws/ eBayISAPI.dll?ViewItem&category=31745&item=5917131317&rd=1
Brent Watson can attest to the benefits of observing from 20 feet off of the ground. The seeing is always steadier from such heights. Those with vertigo will stay away so lines for your scope will be shorter. You can get away with a very small secondary obstruction too and collimation is a cinch. No need for the correction of Naglers or a Paracorr either. Of course you need a flatbed to transport both the tube, counterweight, and extension ladder.
Remember, look with both eyes for best effect when viewing a first quarter moon from a dozen steps up the ladder. Those purple crescents make for a great trip!
dlb
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Before you make a final decision you might talk to Rick Singmaster with Starmaster Telescopes http://www.starmastertelescopes.com/ he makes the 20" f/4.3 with Zambuto mirror. He uses small diagonals with a low profile focuser so you may not have an increased central obstruction. He also has the following to say about enchased coatings on the primary mirror: Starmaster "primary mirror coatings utilize Ion-Assisted Deposition (IAD) and quartz overcoat. This provides higher reflectivity than the "standard" 89% sputtered coatings. Using a single IAD metallic layer also eliminates the tendency of multilayer "enhanced" metallic coatings to roughen the mirror surface thereby degrading the image. We believe that the fidelity of the optical images are better preserved with this process, with the additional assurance that the optical coatings will outlast "run of the mill" SiO-overcoated (monoxide, not the superior quartz) sputtered coatings." I have had personal experience with enhanced coatings degrading the performance on my 10" mirror. My Cave mirror was much better before having it recoated. The f/4.3 Starmaster also is balanced with a 2" Paracorr which Rick highly recommends. It gives a greater than 10 fold improvement in the coma free diffraction limited field in an f/4.3 scope. Stars are sharp to the edge in my 14 mm Ultrawide eyepiece. I haven't really tested my other eyepieces. Of course Starmasters cost mote than Obssesions so that may be an important factor. Clear Skies Don Colton -----Original Message----- From: utah-astronomy-bounces+djcolton=piol.com@mailman.xmission.com [mailto:utah-astronomy-bounces+djcolton=piol.com@mailman.xmission.com]On Behalf Of Debbie Sent: Monday, August 30, 2004 11:55 AM To: Utah Astronomy Subject: RE: [Utah-astronomy] f/4 or f/5? Why not try... If I decide to upgrade, I'll think I'll go with the f/5 version. There is less of a central obstruction with the f/5 than the f/4.5. An f/4 has too much coma and is harder to collimate. The image size is a little bigger with the f/5 version. And the Paracorr is not necessary. For Dave Kriege, the f/5 is a "no brainer". I'm thinking about purchasing a trailer first before upgrading. I want to be able to view with my refractor and my reflector plus have room for sleeping bags and such. The Kolob Reservoir site is about an hour and twenty minutes from my house so I think it is wiser to sleep up there until morning. Debbie ps missed you up at Wolf Creek Pass. It was very cool and confortable up there. I may just head up there next month
[Original Message] From: David L Bennett <dlbennett@mac.com> To: <utah-astronomy@mailman.xmission.com>; Association Utah <uvaa@mailman.xmission.com> Date: 8/30/2004 10:08:30 AM Subject: [Utah-astronomy] f/4 or f/5? Why not try...
Why not go for a 16" f/16.5? See the mirror being offered at:
http://cgi.ebay.com/ws/ eBayISAPI.dll?ViewItem&category=31745&item=5917131317&rd=1
Brent Watson can attest to the benefits of observing from 20 feet off of the ground. The seeing is always steadier from such heights. Those with vertigo will stay away so lines for your scope will be shorter. You can get away with a very small secondary obstruction too and collimation is a cinch. No need for the correction of Naglers or a Paracorr either. Of course you need a flatbed to transport both the tube, counterweight, and extension ladder.
Remember, look with both eyes for best effect when viewing a first quarter moon from a dozen steps up the ladder. Those purple crescents make for a great trip!
dlb
_______________________________________________ Utah-Astronomy mailing list Utah-Astronomy@mailman.xmission.com http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy Visit the Photo Gallery: http://www.utahastronomy.com
_______________________________________________ Utah-Astronomy mailing list Utah-Astronomy@mailman.xmission.com http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy Visit the Photo Gallery: http://www.utahastronomy.com
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Debbie -
Don J. Colton