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#1
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Orion "clear aperture" 3.6 reflector?
The last couple of Orion catalogs have featured this "SkyView Pro 3.6CA
Reflector". I haven't seen any reviews on this scope- does anyone know of any? And does a reflector made this way really have the additional advantages they discuss and why haven't I seen this in larger apertures? Thanks, Bill |
#2
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It's an off-axis Newtonian design that's been available from several
companies. In theory, you get the performance of an APO refractor because there is no obstruction from the secondary mirror. But you also get the coma inherent with any newtonian design and the focal ratio is higher than most APOs these days. This makes it primarily a visual instrument. You haven't seen larger apertures because the mirror is literally cut (think cookie dough) out of a parabolic blank at least twice as big. To make the 3.6" mirror for this scope, they probably start with a 12", f/4 mirror and cut 4-6 smaller mirrors from it. Bill Ryan wrote: The last couple of Orion catalogs have featured this "SkyView Pro 3.6CA Reflector". I haven't seen any reviews on this scope- does anyone know of any? And does a reflector made this way really have the additional advantages they discuss and why haven't I seen this in larger apertures? Thanks, Bill |
#3
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"Tim Killian" wrote in message ... It's an off-axis Newtonian design that's been available from several companies. In theory, you get the performance of an APO refractor because there is no obstruction from the secondary mirror. But you also get the coma inherent with any newtonian design and the focal ratio is higher than most APOs these days. This makes it primarily a visual instrument. That's unfortunate. I guess then it would make better sense to spend $350 more for their 100mm apo refractor ota. Bill You haven't seen larger apertures because the mirror is literally cut (think cookie dough) out of a parabolic blank at least twice as big. To make the 3.6" mirror for this scope, they probably start with a 12", f/4 mirror and cut 4-6 smaller mirrors from it. Bill Ryan wrote: The last couple of Orion catalogs have featured this "SkyView Pro 3.6CA Reflector". I haven't seen any reviews on this scope- does anyone know of any? And does a reflector made this way really have the additional advantages they discuss and why haven't I seen this in larger apertures? Thanks, Bill |
#4
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Actually it's more like $999 for the 100mm APO OTA.
http://www.telescope.com/shopping/pr...roductID=54904 |
#5
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Hi Bill,
I originally introduced this design about 7 years ago (DGM Optics). If you browse my site you will see that I do offer larger scopes and/or optics sets. This type of scope is made by cutting 4 smaller off-axis paraboloids from a larger parent mirror. In order to produce my scopes at around F/10 we start with a 10.25" f/4 parent. The off-axis sections are cut out at a point where they are decentered just enough for the incoming light to not obstruct the tip of the secondary but are kept about .25" from the outside edge of the parent mirror. If you browse the below links to user reviews, you`ll find that, contrary to popular mythology, coma is not a problem with these scope even using the F/4 parent mirror. I would also mention that the Orion scopes are significantly different than my scopes in several regards; 1. F/10 (DGM) vs F/13 (Orion) 2. Orion optics are most likely an "off the shelf" 10" f/4.8, quality unknown. 3. DGM optics by Dodgen Optical. I`ll let the user reviews speak to quality of the scopes. http://users.erols.com/dgmoptics/OA-4%20review.htm http://users.erols.com/dgmoptics/Customer.htm http://www.scopereviews.com/page1m.html#3 http://www.scopereviews.com/page1f.html#3 http://www.cloudynights.com/reviews/oa4.htm http://www.cloudynights.com/reviews/oa42.htm http://www.excelsis.com/1.0/section....&findtext=&con d=&range=d&archive=-1&range=d Dan McShane www.dgmoptics.com http://groups.yahoo.com/group/offaxis/ Bill Ryan wrote in message nk.net... The last couple of Orion catalogs have featured this "SkyView Pro 3.6CA Reflector". I haven't seen any reviews on this scope- does anyone know of any? And does a reflector made this way really have the additional advantages they discuss and why haven't I seen this in larger apertures? Thanks, Bill |
#6
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Tim Killian wrote in message ... It's an off-axis Newtonian design that's been available from several companies. In theory, you get the performance of an APO refractor because there is no obstruction from the secondary mirror. But you also get the coma inherent with any newtonian design and the focal ratio is higher than most APOs these days. Tim, reports of coma being problematic are all but nil from actual user/owners of OANs. This makes it primarily a visual instrument. These are fine scope imaging wise as long as you stick to lunar, planetary, or solar. You haven't seen larger apertures because the mirror is literally cut (think cookie dough) out of a parabolic blank at least twice as big. To make the 3.6" mirror for this scope, they probably start with a 12", f/4 mirror and cut 4-6 smaller mirrors from it. For my 98mm F/10 OANs we start with a 10.25 F/4 and get 4 OA paraboloids. Also they don`t get cut out until the "parent mirror" is fully polished and figured. Dan McShane Bill Ryan wrote: The last couple of Orion catalogs have featured this "SkyView Pro 3.6CA Reflector". I haven't seen any reviews on this scope- does anyone know of any? And does a reflector made this way really have the additional advantages they discuss and why haven't I seen this in larger apertures? Thanks, Bill |
#7
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The coma in these OA scopes would be exactly the same as the f/4 parent
mirror. If you're in the center of the FOV, it's not a problem. Off axis is another story. Dan McShane wrote: Tim Killian wrote in message ... It's an off-axis Newtonian design that's been available from several companies. In theory, you get the performance of an APO refractor because there is no obstruction from the secondary mirror. But you also get the coma inherent with any newtonian design and the focal ratio is higher than most APOs these days. Tim, reports of coma being problematic are all but nil from actual user/owners of OANs. This makes it primarily a visual instrument. These are fine scope imaging wise as long as you stick to lunar, planetary, or solar. |
#8
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Dan,
An interesting discussion on the construction of modern OAN's but isnt this an ancient design used at long f ratio as far back as the 1800's? I seem to remember a picture of one with a bipod set of legs at the eyepiece end so it could be proped up in one of the ATM books. Bill Bambrick 41 N, 73 W, 95 ASL |
#9
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You might be confusing it with the large Herschellian (e.g. Lord Rossi)
reflectors used in the 1800s. They have the eyepiece at prime focus off to one side of the scope. Jb2269 wrote: Dan, An interesting discussion on the construction of modern OAN's but isnt this an ancient design used at long f ratio as far back as the 1800's? I seem to remember a picture of one with a bipod set of legs at the eyepiece end so it could be proped up in one of the ATM books. Bill Bambrick 41 N, 73 W, 95 ASL |
#10
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On Wed, 02 Feb 2005 10:47:29 -0700, Tim Killian
wrote: It's an off-axis Newtonian design that's been available from several companies. In theory, you get the performance of an APO refractor because there is no obstruction from the secondary mirror. Un, no. Any obstructed scope with an obstruction under about 15% performs almost like it had no obstruction but, NO reflector I've ever seen produces images like the best apos, inch per inch, unobstructed or not. The use of a "sector" of a larger paraboloid is interesting, but it not a perfect sub for an apo, despite the high price. -Rich |
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