· Get a Cloudy Nights T-Shirt · Submit a Review / Article    Click here if you are having trouble logging into the forums Cloudy Nights - Official Forums of the 2009 International Year of Astronomy Privacy Policy | Please read our Terms of Service | Signup and Troubleshooting FAQ | Problems? PM a Red or a Green Gu.... uh, User   You are not logged in. [Login] Forum Archives · Entrance · Main Index · Search · New user · Who's Online FAQ · Calendar Equipment Discussions >> ATM, Optics and DIY Forum Previous   Index   Next   Flat   Houdini professor emeritus Reged: 07/13/07 Posts: 523 Loc: Europe Re: How Good a Secondary is needed?       07/03/09 08:42 AM Edit   Reply   Quote   Quick Reply:   Mike, Try a 16" f/5 with a 3.1" diagonal 12.6" from focus (my current planetary "grab & go" scope). Assuming a perfect primary and a 1/10 wave P-V diagonal curvature, how much astigmatism does one get? I'm asking the question because this page claims that you can have 4 or 5 waves of curvature on the diagonal without problem. Robert -------------------- 16" f/4.9 motorized alt-az, 25" f/5 Dobson, 43" f/4 alt-az under construction Mirror Edge Support Calculator Post Extras       Entire thread Subject Posted by Posted on How Good a Secondary is needed? gaz-in 07/02/09 04:49 PM Re: How Good a Secondary is needed? Mike I. Jones   07/03/09 11:00 AM Re: How Good a Secondary is needed? Mark Harry   07/03/09 01:09 PM Re: How Good a Secondary is needed? gaz-in   07/03/09 12:01 PM Re: How Good a Secondary is needed? bbasiaga   07/02/09 05:02 PM Re: How Good a Secondary is needed? llanitedave   07/02/09 06:40 PM Re: How Good a Secondary is needed? Bird   07/02/09 09:41 PM Re: How Good a Secondary is needed? Mike I. Jones   07/02/09 10:13 PM Re: How Good a Secondary is needed? Houdini   07/03/09 06:19 AM Re: How Good a Secondary is needed? Mike I. Jones   07/03/09 08:14 AM Re: How Good a Secondary is needed? Houdini   07/03/09 08:42 AM Re: How Good a Secondary is needed? jayscheuerle   07/03/09 10:52 AM Re: How Good a Secondary is needed? Mark Harry   07/03/09 07:28 AM Re: How Good a Secondary is needed? Mark Harry   07/03/09 07:34 AM Re: How Good a Secondary is needed? walt r   07/02/09 11:55 PM Extra information 5 registered and 3 anonymous users are browsing this forum. Moderator:  Don W, Mike I. Jones  Forum Permissions       You cannot start new topics       You cannot reply to topics       HTML is disabled       UBBCode is enabled Rating: Thread views: 346 Jump to *International Year of Astronomy 2009* -----   Global Coordination   Cornerstone Projects   Special Projects   Special Task Groups   Global Activities   National and Regional Activities   IYA 2009 in Africa   IYA 2009 in the USA*Announcements and News* -----   Cloudy Nights Announcements   Discussion of CN Articles, Reviews, and Reports   Beginners Forum   Celestial Events   Light Pollution*Equipment Discussions* -----   ATM, Optics and DIY Forum   Binoculars   Binoviewers   Cats & Casses   Classic Telescopes   Equipment   Eyepieces   Mounts   Observatories   Reflectors   Refractors    Celestron SkyScout and Meade mySky   Video and Electronically Assisted Astronomy*Astrophotography and Sketching* -----   Beginning and Intermediate Imaging   Film Astrophotography   DSLR & Digital Camera Astro Imaging & Processing   CCD Imaging & Processing   Solar System Imaging & Processing   Sketching   Astro Imaging/Sketching Contest *Observing* -----   NEO   General Observing   Planetary and Solar System Observing   Lunar Observing   Deep Sky Observing   Double Star Observing   Solar   Variable Star Observing and Radio Astronomy*Telescope Specific Forums* -----   Celestron NexStar    NexStar GPS / CPC Telescopes   Questar Forum   Meade ACF/RCX / LX / GPS    Meade ETX*Other* -----   Science of Astronomy & Space Exploration   AstroWebsites   Space Rocks*Speciality Forums* -----   AstroArt   Astronomy Software & Computers   Stellar Media   Astro Outreach, Clubs and Star Parties*CN Feedback and Vendor Announcements* -----   Vendor and Group Announcements CN Forums Home

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