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 >> Reflectors Previous   Index   Next   Threaded   Pages: 1 danner super member Reged: 02/27/07 Posts: 141 Loc: Bay Area, Cali What does it mean if the view is "soft"       #1563204 - 04/24/07 01:47 AM Edit   Reply   Quote Quick Reply   on the outer edge of view but sharp in the middle out to 85% of the field of view? I take it to mean the focus is not sharp on the outer edge. What causes that? Astigmatism? -------------------- XT8 Custom 10" f/4.5 Dob Nagler's dot the i and cross the t. Coe Montebello Coyote Post Extras:       R_Angkasa scholastic sledgehammer Reged: 02/16/06 Posts: 899 Loc: SO PAS - CA Re: What does it mean if the view is "soft" [Re: danner]       #1563228 - 04/24/07 02:06 AM Edit   Reply   Quote Quick Reply   It is called curvature . . . usually caused by your EP. Astigmatism is when you make the star image out of focus the form is elliptical (it should be perfect circle). And when you rack the focuser in and out, the ellipse inside focus is 90 degrees to the outside focus. -------------------- 10x42L IS FS128 12" DSH 3.5, 5, 7, 10, 14, 20, 30, 40 Post Extras:       danner super member Reged: 02/27/07 Posts: 141 Loc: Bay Area, Cali Re: What does it mean if the view is "soft" [Re: R_Angkasa]       #1563250 - 04/24/07 02:34 AM Edit   Reply   Quote Quick Reply   Thanks. -------------------- XT8 Custom 10" f/4.5 Dob Nagler's dot the i and cross the t. Coe Montebello Coyote Post Extras:       KWB Postmaster Reged: 09/30/06 Posts: 7634 Loc: Westminster,Co Elev.1646Meters Re: What does it mean if the view is "soft" [Re: danner]       #1563268 - 04/24/07 03:09 AM Edit   Reply   Quote Quick Reply   I disagree. To me it means a view with noticeably less contrast and definition/sharpness. That's a simplistic answer. Astigmatism and FC are different matters. I don't equate them to "soft". Kenny -------------------- Kenny "When dealing with a mystery,choose the most unlikely of the likely possibilities"-Sherlock Holmes Edited by KWB (04/24/07 03:24 AM) Post Extras:       BluewaterObserva Post Laureate Reged: 05/18/04 Posts: 4763 Loc: Zuni Mtns, NM Re: What does it mean if the view is "soft" [Re: KWB]       #1563277 - 04/24/07 03:35 AM Edit   Reply   Quote Quick Reply   Your eye piece may be contributing. Might it be coma? coma is a natural abberation of the parabola. Hard to tell from the description. Post Extras:       EdZ Professor EdZ Reged: 02/15/02 Posts: 12581 Loc: Cumberland, R I , USA42N71.4W Re: What does it mean if the view is "soft" [Re: BluewaterObserva]       #1563382 - 04/24/07 06:39 AM Edit   Reply   Quote Quick Reply   It could be a number of things. It could also be several things happening at once. WHAT DO ABERRATIONS LOOK LIKE ON_AXIS Generally, not all aberrations are seen on-axis. The on-axis image created by aberrations is as follows: curvature not seen on-axis. coma not seen on-axis. If the stars seem never to focus to a fine point, but at best remain slightly bloated and are still circular, and it cannot be focused out it is probably spherical aberration. If the star seems to not come into sharp focus it may be astigmatism. If astigmatism is severe, then on-axis focused images will show a very small cross, never a fine pinpoint. Passing in and out of focus will show the out-of-focus image to flip orientation by 90°. Longitudinal CA will produce softness of image focus of perfectly on-axis objects because all colors in the spectrum will not come to focus at the same point. Sometimes seen as a small circular band of color arounnd a finely focused star point. OFF_AXIS As for how you notice stars in the outer fov, the image created by aberrations is as follows: If the star seems slightly bloated, but it can be refocused down to a finer point, then it is curvature. If the stars seem flared as wedges with the point towards the middle and the flared wedge toward the outer edge, then it is coma. It cannot be focused out. If the stars seem slightly bloated but are still circular, and it cannot be focused out it is spherical aberration. If the star seems slightly bloated and slightly elongated than it is astigmatism. Astigmatism will show elongated images off axis. If astigmatism is severe, then on-axis focused images will show a very small cross, never a fine pinpoint. If you have both astigmatism and coma, the off axis images will look like comets with an oblong axis, or like seagulls. Longitudinal CA will produce softness of image focus of perfectly on-axis objects because all colors in the spectrum will not come to focus at the same point. Lateral CA will produce color fringes around all bright objects when viewed slightly off axis, but you should see a different color towards the lens center than you see towards the lens edge. edz -------------------- Teach a kid something today. The feeling you'll get is one of life's greatest rewards. member#21 Post Extras:       csa/montana Astro Ambassador Reged: 05/14/05 Posts: 28613 Loc: montana Re: What does it mean if the view is "soft" [Re: EdZ]       #1563541 - 04/24/07 09:31 AM Edit   Reply   Quote Quick Reply   Edz: Thanks for posting this great explanation. This would be a good post to "sticky" at the top of the forum, so it doesn't get buried. Carol -------------------- Carol AstroTech 16" Dob (Thanks ASTRONOMICS!) AstroTech 66ED / Vixen 80MF/AstroTech Voyager Masuyama's 7.5, 15, 25W, 35mm, Tak LE 5mm B/TMB 3.2 7mm Pentax XL, 10mm Pentax XW 14mm Meade 4000 UWA 22mm Pan, 35mm Pan DreamCatcher Dobservatory, #2 Post Extras:       werewolf6977 Lord High Smasher Reged: 12/15/03 Posts: 7444 Loc: Hanover, Ohio Re: What does it mean if the view is "soft" [Re: csa/montana]       #1563566 - 04/24/07 09:45 AM Edit   Reply   Quote Quick Reply   I'll go ahead and make it sticky now -------------------- Pete 6" Apogee/LXD55 - "The Beast" Starhopper 6" Dob - "Shiva" Spaceprobe 130 EQ - "Spacey" Bushnell Fatboy The Abomination Sun Pak Pro 7500 Platinum Edition 10X25 Bushnell Camo Roofies 7X35 Tasco Classic Plastic (good views though) 7X42 Tasco Rare Bird 10X50 Nikon Actions (Type 7) 15X70 Skymasters - "DroolMeisters" One ratty old IBM 600E LapTop Post Extras:       csa/montana Astro Ambassador Reged: 05/14/05 Posts: 28613 Loc: montana Re: What does it mean if the view is "soft" [Re: werewolf6977]       #1563729 - 04/24/07 11:32 AM Edit   Reply   Quote Quick Reply   Thanks Pete! Edz explanation is the best I've seen to explain all of this. This will give us something to refer others to read. Carol -------------------- Carol AstroTech 16" Dob (Thanks ASTRONOMICS!) AstroTech 66ED / Vixen 80MF/AstroTech Voyager Masuyama's 7.5, 15, 25W, 35mm, Tak LE 5mm B/TMB 3.2 7mm Pentax XL, 10mm Pentax XW 14mm Meade 4000 UWA 22mm Pan, 35mm Pan DreamCatcher Dobservatory, #2 Post Extras:       FebStars scholastic sledgehammer Reged: 02/02/06 Posts: 796 Loc: MA Re: What does it mean if the view is "soft" [Re: csa/montana]       #1584040 - 05/03/07 07:34 PM Edit   Reply   Quote Quick Reply   Thanks, Ed Z.! Great explanation! Tom -------------------- Tom H Meade SN10 Orion ED80 Orion ED100 AstroTech66 Televue Genesis 500mm Garrett Gemini LW 20x80 Binocs Orion EQ-G, LXD75 Mounts "The cure for boredom is curiousity. There is no cure for curiousity." Post Extras:       werewolf6977 Lord High Smasher Reged: 12/15/03 Posts: 7444 Loc: Hanover, Ohio Re: What does it mean if the view is "soft" [Re: FebStars]       #1584399 - 05/03/07 10:59 PM Edit   Reply   Quote Quick Reply   Ed's the man!! -------------------- Pete 6" Apogee/LXD55 - "The Beast" Starhopper 6" Dob - "Shiva" Spaceprobe 130 EQ - "Spacey" Bushnell Fatboy The Abomination Sun Pak Pro 7500 Platinum Edition 10X25 Bushnell Camo Roofies 7X35 Tasco Classic Plastic (good views though) 7X42 Tasco Rare Bird 10X50 Nikon Actions (Type 7) 15X70 Skymasters - "DroolMeisters" One ratty old IBM 600E LapTop Post Extras:       karim super member Reged: 11/09/05 Posts: 129 Loc: HB, California Re: What does it mean if the view is "soft" [Re: csa/montana]       #1997286 - 11/20/07 01:52 AM Edit   Reply   Quote Quick Reply   I must be lucky, I have never experienced any of these symptoms. I have a C8 and use 13mm T6 9mm T6 7.5 mm Parks golden Series 2x Parks Barlow -------------------- http://www.eyepiecereviews.com Post Extras:       mnpd professor emeritus Reged: 06/28/05 Posts: 619 Loc: Nashville, Tennessee Re: What does it mean if the view is "soft" [Re: karim]       #2573654 - 08/11/08 02:49 AM Edit   Reply   Quote Quick Reply   Speaking non-technically, to me a "soft" view means you are turning the focus knob on an out-of-focus object to bring it into focus. Before you get to that crisp image we all like so much, the focus starts moving out-of-focus the other way. Optics, atmosphere... different causes. -------------------- Tom 12" f/5 Orion 12XTi 8" f/6 Orion 8XT 8" f/4 Homebuilt Newt 6" f/8 Homebuilt Newt 5" f/9 Meade Achro 90mm f/11 Homebuilt Achro 80mm f/10 Homebuilt Solar Achro 80mm f/5 Homebuilt "Shorty" Achro 60mm Refractors (many, assorted) 20x80 Konus Binoculars 10x50 Leupold Binoculars Post Extras:       Dylan Gladstone scholastic sledgehammer Reged: 08/05/07 Posts: 955 Loc: Connecticut, USA Re: What does it mean if the view is "soft" [Re: mnpd]       #2588788 - 08/18/08 04:22 PM Edit   Reply   Quote Quick Reply   I think I've experienced all of these with my eyes if I take off my glasses. -------------------- Orion SkyView Pro 127mm Maksutov Post Extras:       lymorkiew45 sage Reged: 12/30/07 Posts: 323 Loc: Anaheim Re: What does it mean if the view is "soft" [Re: Dylan Gladstone]       #2589718 - 08/18/08 11:53 PM Edit   Reply   Quote Quick Reply   Me too...clear skies -------------------- Control Yourself, let others do as they will, this does not mean you are weak, control your heart, obey the principles of life, this does not mean others are stronger. *Lung Ying Mor Kiew motto* Starfinder 16 EQ, and dob DS-10 Orion XT 12i Z12 All the Lanthanum superwides! Orion ultrablock filter 9mm Nagler type 6 15mm, 25mm, 35mm Ultrascopics Orion Shorty Plus barlow Orion Lazer Colimator 30" dob planned out in far future! Post Extras:       Pages: 1 Previous   Index   Next   Threaded   Extra information 31 registered and 14 anonymous users are browsing this forum. 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