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llanitedave
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Joined: 16 Feb 2008
Posts: 473
Location: Amargosa Valley, NV
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 Posted: Mon Nov 17, 2008 8:36 pm Post subject: Sauron's Other Eye |
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Time for the official introduction!
I've used it twice now, but its still not 100%. I've got it down now for some stiffening modifications and some work on the mirror cell to make collimation easier. Tomorrow is "third light", and I think that will be the charm!
Here's Elaine's introduction:
This is the top end, showing the wire spider. That's working surprisingly well.
And here's the bottom end, showing the center mounted conical mirror. It takes 35 pounds of counterweights to keep the center of gravity low enough for this short rocker box. Whether that's worth it will be found out as I use it.
Still needs some tweaks, but overall I'm pretty happy with it.
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Erik
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Joined: 12 Feb 2008
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Location: Big Island of Hawaii On the slope of Mauna Loa 4500 feet mag 7 sky :)
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| Posted: Mon Nov 17, 2008 8:58 pm Post subject: |
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Wow, very nice, Dave!!! 
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-Erik Wilcox
Homebuilt 16" Truss Dob
SV 80mm ED Nighthawk NG on M1 ALT/AZ
Nikon Prostaff 65mm spotter on Trekpod
Konusvue 20x80 binos/Peterson pipemount
Orion 10x50 binos
Homebuilt 80mm f/5 refractor
Mirador 60mm f/12 1960's refractor
Evolution is both fact and theory. Creationism is neither. -Anonymous |
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Gary
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Joined: 14 Feb 2008
Posts: 113
Location: USA Louisiana
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| Posted: Tue Nov 18, 2008 5:18 am Post subject: |
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Wow indeed Dave! Very nice! Love the design, including the paint scheme.
I'm sure more questions will come to mind eventually, but for now, how do you adjust collimation at the secondary. I could see enough from my computer screen to tell how it's suspended, but not fully how you adjust it.
Gary |
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Chopin
The Grand Mustachio
Joined: 18 Mar 2008
Posts: 842
Location: a place or situation occupied.
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| Posted: Tue Nov 18, 2008 6:46 am Post subject: |
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Dave, just gorgeous! The color, the unique box design, the conical mirror, the wire spider...it's the whole package. I absolutely love the box design, with the circular bearing that almost resembles the joint of an elbow or knee. Holy cow!
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ŠJason
"A word to the wise isn't necessary, it is the stupid ones who need all the advice."
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llanitedave
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Joined: 16 Feb 2008
Posts: 473
Location: Amargosa Valley, NV
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| Posted: Tue Nov 18, 2008 9:53 am Post subject: |
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| Gary wrote: | Wow indeed Dave! Very nice! Love the design, including the paint scheme.
I'm sure more questions will come to mind eventually, but for now, how do you adjust collimation at the secondary. I could see enough from my computer screen to tell how it's suspended, but not fully how you adjust it.
Gary |
Here's a schematic:
The basic support is a pvc pipe with a piece of plywood that mounts a 5/16" bolt. The bolt passes through a rubber grommet that supports the weight of the secondary (that's the the black rectangle in the picture) and absorbs vibrations. It's a pretty tight fit, which is good. The bolt is nested inside a smaller length of pvc, which is drilled to accept three small bolts penetrating radially. One of them is shown in the graphic. These adustment bolts press against a regular hex nut that's mounted on the threads of the main support bolt.
The advantage of this system is that the swivel point for the secondary is closer to the centerline of the mirror face than most secondary adjustment points. This way when you adust the angle of the mirror, there is less lateral movement to compensate for. Also, the central nut and bolt arrangement allows for easy rotation if necessary, and a straightforward method of centering the secondary longitudinally.
There are a number of design flaws in the structure of this scope, but the secondary arrangement is one of the things that is working out well. I like it enough to want to use it when I redo my 10", and if I ever build a bigger scope, I think I'll stick with it.
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Gary
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Joined: 14 Feb 2008
Posts: 113
Location: USA Louisiana
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| Posted: Tue Nov 18, 2008 1:05 pm Post subject: |
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Very nice Dave! The advantages of the design are obvious (now that you describe them;-) Please keep us updated on any future tweaks.
Thanks.
Gary |
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Erik
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Joined: 12 Feb 2008
Posts: 3089
Location: Big Island of Hawaii On the slope of Mauna Loa 4500 feet mag 7 sky :)
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| Posted: Tue Nov 18, 2008 8:08 pm Post subject: |
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Now you've got me thinking about tweaking my design on my new dob project.
Man, that is sweet!
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-Erik Wilcox
Homebuilt 16" Truss Dob
SV 80mm ED Nighthawk NG on M1 ALT/AZ
Nikon Prostaff 65mm spotter on Trekpod
Konusvue 20x80 binos/Peterson pipemount
Orion 10x50 binos
Homebuilt 80mm f/5 refractor
Mirador 60mm f/12 1960's refractor
Evolution is both fact and theory. Creationism is neither. -Anonymous |
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Chopin
The Grand Mustachio
Joined: 18 Mar 2008
Posts: 842
Location: a place or situation occupied.
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| Posted: Tue Nov 18, 2008 8:58 pm Post subject: |
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Dave, not only does collimation of the secondary in your design cause less impact on optical axis shift, but it has a better center of gravity in regards to weight distribution. I imagine it will actually hold collimation better than a standard design. Intruiging. I like.
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ŠJason
"A word to the wise isn't necessary, it is the stupid ones who need all the advice."
--Bill Cosby |
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llanitedave
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Joined: 16 Feb 2008
Posts: 473
Location: Amargosa Valley, NV
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| Posted: Wed Nov 19, 2008 6:58 pm Post subject: |
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I really like the mechanicals of the support so far. I'm not quite as confident about the wire arrangement yet. I guess I won't know until it's stretched as much as it will stretch and holds its tension for a reasonable period.
I must admit, though, it's very quick and easy to tighten when the tension does decrease.
I think I still need to work some on the mirror cell. There's definite collimation shift that I don't think is coming from the secondary, although I haven't ruled out the truss structure yet either.
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snorkler
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Joined: 13 Feb 2008
Posts: 2428
Location: Bay Area, California
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| Posted: Wed Nov 19, 2008 9:25 pm Post subject: |
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She's a beauty, Dave.
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