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] Entrance · Main Index · Search · New user · Who's Online FAQ · Calendar Equipment Discussions >> ATM, Optics and DIY Forum Previous   Index   Next   Threaded   Pages: 1 refractory Pooh-Bah Reged: 02/05/05 Posts: 1016 Light loss in optically clear flat when angled?       #2583682 - 08/15/08 06:03 PM Edit   Reply   Quote Quick Reply   Lets suppose I've got an optical flat made from optically clear glass, made elliptical for use at 45 degrees, mirror-coated but with an elliptical uncoated spot in the center. If both faces of the flat are parallel, and the flat is relatively thin, then I shouldn't lose too much light to transmission, but what about reflection? Will antireflection coating on the unmirrored spot help, or is the angle too steep? Jess Tauber Post Extras:       DAVIDG Pooh-Bah Reged: 12/02/04 Posts: 1458 Loc: Hockessin, De Re: Light loss in optically clear flat when angled? [Re: refractory]       #2583744 - 08/15/08 06:41 PM Edit   Reply   Quote Quick Reply   It depends on the refraction index of the glass to get an exact number but a good estimate will be that the glass will reflect about 5% of the light and transmit about 95%. AR coating will increase it around 98%. - Dave -------------------- Homemade 'scopes 8"f/7,6" f/5", 6"f/4, 4.25" Schief. 60mm Coronagraph,60mm H-alpha system, 4.25" White-light Solar Newtonian,solar spectroscope, 4.5" f/16 Schupmann Medial refractor, 14 Stellafane awards 7 in optics Engineering = Taking what you have and making what you need. Post Extras:       John Carruthers Skiprat Reged: 02/02/07 Posts: 1708 Loc: Kent, UK Re: Light loss in optically clear flat when angled? [Re: refractory]       #2584439 - 08/16/08 03:02 AM Edit   Reply   Quote Quick Reply   Try putting a clear piece of glass in front of your secondary, you'll get a double image, the same may happen with any parallel unsilvered glass. A small angled between the faces will take care of the reflected double image, like a Herschel wedge. -------------------- Jc ATM 10" F6.1, 1/25th wave spec (max wavefront error +/- 1/12.6 in zone 4 of 6, sodium light ) 6" F7 spec 127mm F9.4 Refractor 10 x 50 bin ETX80 (finder) Canon 20D and a curious mind Post Extras:       Ed Jones Pooh-Bah Reged: 04/06/04 Posts: 1084 Loc: Sin-sin-atti Re: Light loss in optically clear flat when angled [Re: John Carruthers]       #2584680 - 08/16/08 09:23 AM Edit   Reply   Quote Quick Reply   I'm not sure what you are doing here. If you have an unsilvered spot on your diagonal it won't see any light on axis anyway, only off axis light. Are you meaning to transmit through this spot? It will be astigmatic. -------------------- Ed Jones Post Extras:       Pages: 1 Previous   Index   Next   Threaded   Extra information 7 registered and 3 anonymous users are browsing this forum. Moderator:  Don W, Joe Cipriano  Print Thread Forum Permissions       You cannot start new topics       You cannot reply to topics       HTML is disabled       UBBCode is enabled Thread views: 134 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 Imaging   Film Astrophotography   DSLR & Digital Camera Astro Imaging & Processing   CCD Imaging & Processing   Solar System Imaging & Processing   Sketching   Astro Imaging/Sketching Contest *Observing* -----   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 Home

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