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DSalters
scholastic sledgehammer
Reged: 03/03/07
Posts: 866
Loc: High Ridge, MO (St. Louis)
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Is there any reason a 2" forcuser and 2" EPs would not work on a 4.5" dob? There's likely a very simple answer to this, but I can't decide why it wouldn't work if balance is not an issue.
Thanks for the input,
Daniel
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Daniel Salters
Celestron C5
Bushnell Voyager 6" Dob
13" Dob (Under Construction)
EPs: Baader Hyperions and TMB Planetaries
"The sun has one kind of splendor, the moon another and the stars another; and star differs from star in splendor." -1 Corinthians 15:41
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Houdini
professor emeritus
Reged: 07/13/07
Posts: 579
Loc: Europe
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You would need a relatively large secondary mirror to get some decent illumination at the edge of the field of a 2" focuser.
Robert
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16" f/4.9 motorized alt-az, 25" f/5 Dobson, 43" f/4 alt-az under construction
Mirror Edge Support Calculator
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MMICKELS
Aluminum Knight
Reged: 01/20/04
Posts: 28973
Loc: The Land of Shake and Bake
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Best to stick with 1.25" EP's on a scope of that size. Like Robert stated you won't be able to make use of the larger FOV afforded by the 2" EP's unless you have a way oversize secondary mirror, and then you will lose contrast.
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Mark
"Never eat more than you can lift"
Miss Piggy
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Art Bianconi
Post Laureate
Reged: 03/06/06
Posts: 4659
Loc: Delaware River Valley, New Jer...
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Hi mark, Hi Dan
When first learning about sleds, Mark enlightened me about how their advantage is that they get the EP much closer to the secondary.
My recent success with the barrel style "sled" focuser makes me wonder if both your answers would still apply to a sled focuser.
I'm contemplating the same "sled" design on two different scopes: a 100mm and a 6"
Thanks
Art
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“Everything is on its way to somewhere. . . . . everything!"
____________________ George Malley (John Travolta)
________________________ "Phenomenon"
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RRavneberg
professor emeritus Rest in Peace 19xx-2009
Reged: 12/02/05
Posts: 634
Loc: Columbus, OH
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Many 2" modern eyepieces are essentially 1.25" eyepieces with an optional 2" barrel. Check your eyepieces; if the field lens is smaller than 1.25", there's little to be gained by using a 2" eyepiece.
Sometimes using the 2" barrel can assist in getting the eyepiece closer to the diagonal (as noted in an earlier post).
I use a Vixen LVW22 in my 4.1" f/4.2 RFT (along with an assortment of Radians for higher powers). The Vixen has a 65 degree apparent field, 20mm of eye relief (I can use it with glasses) and a 3.25 degree actual FOV.
And it's all in a small 1.25" helical focuser.
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Ron Ravneberg
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Art Bianconi
Post Laureate
Reged: 03/06/06
Posts: 4659
Loc: Delaware River Valley, New Jer...
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Hello Ron!
You wrote: "Many 2" modern eyepieces are essentially 1.25" eyepieces with an optional 2" barrel."
I've two Vixen Lanthanum's (8mm WA and 17mm WA) Nice EP's. Both have a 1.25" barrel and above that a 2" barrel. I normally use them as 2" devices however, I ran into a problem with my new barrel "Sled" focuser.
Because it's a sled, it has no draw tube. The result is that when used as a two inch, the 1.25" barrels of both Lanthanum's protrude into the light path.
Fortunately, I have enough travel in the focuser to allow the use of the adapter which moves those two EP's out some.
Art
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“Everything is on its way to somewhere. . . . . everything!"
____________________ George Malley (John Travolta)
________________________ "Phenomenon"
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DSalters
scholastic sledgehammer
Reged: 03/03/07
Posts: 866
Loc: High Ridge, MO (St. Louis)
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You bring up an interesting point that I've been wondering about as well...although I am drifting a bit from my original question, I've been wondering about the advantage of using 1.25" eyepieces such as your Vixen shown above or Stratus/Hyperions, etc. What advantages are there in using a 2/1.25" eyepiece in a 2" focuser? It does get the eyepiece closer to the diagonal and would perhaps be steadier (???). As well, it would allow the use of 2" and 1.25" EPs without having to change adapters. Does anyone run into focuser-travel problems (reaching focus) when using their Hyperions, etc. in this manner?
I'm wondering these things because I am building the 4.5" f/8 Dob. mentioned above and in the near future a 10 or 12" Dob. as well. I know I will be fighting a bit with balance issues on the 4.5", but I'm looking at the lightweight Kineoptics HC-1 or HC-2 focusers. I just wonder if I will end up liking using my Hyperions in a 2" focuser or if there's any real advantage to this.
I used way too many words to say/ask not a whole lot there, didn't I?
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Daniel Salters
Celestron C5
Bushnell Voyager 6" Dob
13" Dob (Under Construction)
EPs: Baader Hyperions and TMB Planetaries
"The sun has one kind of splendor, the moon another and the stars another; and star differs from star in splendor." -1 Corinthians 15:41
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MMICKELS
Aluminum Knight
Reged: 01/20/04
Posts: 28973
Loc: The Land of Shake and Bake
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Daniel, you probably only own 1.25" EP's for your 6" dob. I do not see any advantage to going to a 2" focuser for either scope. I can't speak to the Hyperion EP's, but I will tell you that your 75% illuminated field should be near the upper end of your wide field EP's. Anyone should feel free to correct me if I've steered Daniel in the wrong direction.
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Mark
"Never eat more than you can lift"
Miss Piggy
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