Grumpy_one
member
Reged: 03/30/08
Posts: 21
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So I was able to align the primary with the upper cage enough to get some measurements for the poles. Kriege's formula was just about right on. Amazing. So here are the pics for the first daytime first light of my 12.5 f/6.4           
The a-focal shots were done with my DSLR hand held 50mm 1.8 20D Canon. My kids got a chance to see first light. They didn't really get it. But they did see how excited I was. FUN!
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Grumpy_one
member
Reged: 03/30/08
Posts: 21
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The towers are about 2 miles as the crow flys.
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JSeay86
super member
Reged: 04/26/09
Posts: 133
Loc: Norman, OK
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That's a really great looking upper cage. Keep us posted on the progress regarding the truss poles.
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Jared
Orion XX12 Dob
Ten Acre Observatory
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Grumpy_one
member
Reged: 03/30/08
Posts: 21
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I do have question about where the focuser should be. No mention in the book about where it should be, racked in or out. He mentioned putting in an eyepiece with the most inward travel. I'm guessing racked in. I have a two inch tube on my focuser and put it at half way. I tried all the eyepieces and there wasn't that much movement with the cage. I didn't try any barlows. So back to the drawing board on that one. I even put the 31 in thinking that it would have the most impact. Not so much. Thanks
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Grumpy_one
member
Reged: 03/30/08
Posts: 21
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Oh, and I know about the Telrad...
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Achernar
Postmaster
Reged: 02/25/06
Posts: 5025
Loc: Mobile, Alabama, USA
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Nice work! Did you use hardwood dowels for the upper cage struts or are those anodized aluminum tubes? I see you used Baltic Birch plywood too.
Taras
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15-inch F/4.5 Dob under construction
10-inch F/4.5 Discovery Dob
6-inch F/8 Homebuilt Dob
4 1/4-inch F/4 Homebuilt reflector
A whole bunch of eyepieces, filters and other accessories....
Two curious cats
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lightfever
Pooh-Bah
Reged: 09/27/04
Posts: 1276
Loc: Macomb Michigan
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Very nice looking work!
I'm Just about at the same point with my 12.5" f/6.3.
Did you grind the mirror or purchase one?
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Mark
Tasco 15-TE 76mm
Sky Watcher 80mm ED
AT-111 Triplet
XT8i (with Woden re-figured mirror)
Discovery 12.5" f/5 Premium DHQ (PDHQ Split-tube Dobsonian)
12.5" f/6.3 Dob (Underconstruction)
Celestron CG-5GT EQ Mount
Celestron C4 EQ Mount
"Life is not about waiting for the storm to pass, but learning to dance in the rain" unknown
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Grumpy_one
member
Reged: 03/30/08
Posts: 21
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I ground that mirror myself starting in a seminar with John Dobson himself. I finished it in Steve Swayze's shop. The tubes in the upper cage are anodized 1" aluminum tubes.
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Grumpy_one
member
Reged: 03/30/08
Posts: 21
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As it turns out, the ebony star I have is not enough to do the bearings I want. If anyone has any for sale, let me know. I need enough to do 20" bearings. I have a piece
3.75" x 24" to trade or sell. Thanks
Edited by Grumpy_one (10/15/09 04:31 PM)
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Achernar
Postmaster
Reged: 02/25/06
Posts: 5025
Loc: Mobile, Alabama, USA
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Look for any Formica that has a "Touchstone" or "Sparkle" finish, which is what makes Ebony Star as good as it is. The color is unimportant.
Taras
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15-inch F/4.5 Dob under construction
10-inch F/4.5 Discovery Dob
6-inch F/8 Homebuilt Dob
4 1/4-inch F/4 Homebuilt reflector
A whole bunch of eyepieces, filters and other accessories....
Two curious cats
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arpruss
scholastic sledgehammer
Reged: 05/23/08
Posts: 855
Loc: Waco, TX
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About the focuser, I think the advice I was given was that fully racked in, the edge of it should be .25" in from prime focus--if that's not right I'm sure I'll be corrected. (It's easy to find prime focus with Jupiter or the Moon out. Just point scope at the object and put a piece of wax paper outside the focuser hole, moving it in and out until the object is in focus.)
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Coulter Odyssey 13.1" split-tube
Coulter Odyssey 8"
Home-made 7.8" F/4 dobsonian travel scope
Home-made 68mm F/5.3 achro (typically used as finder on 13.1")
Skymaster 15x70
BPTs4 8x30
32mm Plossl, 30mm Rini, 27mm Kellner, 13mm Hyperion, 6mm TMB/BO Planetary, Owl 2X Barlow
Palm TX with AstroInfo and RescoViewer
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dave brock
super member
Reged: 06/06/08
Posts: 165
Loc: Hamilton, New Zealand
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An object 2 miles away will focus further out than one at infinity.
Dave
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20" homebuilt truss dob
6" watson refractor
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Don H
member
Reged: 12/28/06
Posts: 82
Loc: Midwest US
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I usually test and shoot for the focuser half racked out, like you did. There was a post that focus for 2 miles away is further out than infinity, and while I believe that's the the case, I don't think it will be much further in, maybe a 1/4" or so. If you can set it up again on something more distant, you can verify your optimum position and cut your poles with confidence.
If you plan to use a binoviewer, you might want to try and rack your 2" tube further out for normal viewing. That way, if you add a BV, and any OCA, it won't rack inside the edge of your mirror. Or, you could just have a second set of poles and maybe do without an OCA.
By the way, it's all looking great! Please post more pictures as you progress.
Thanks,
Don
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Grumpy_one
member
Reged: 03/30/08
Posts: 21
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So I've decided to go with spilt blocks. We'll see how it works out. Reason I decided to go with split blocks is because of the angle of which the poles would reach the UC.
Solid maple
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