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arpruss
scholastic sledgehammer
Reged: 05/23/08
Posts: 858
Loc: Waco, TX
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I've basically finished (there are always tweaks to be done!) my F/4 7.8" travel scope. I wanted to extend a very big thank you to all the CN folks who gave me a ton of help with various parts of the project, whether by email or by responding to my several posts for help or by selling me the optics for a very low price, as well to TD for helping with the table-saw and router parts of the work (actually, the router only got used to cut out one hole in the focuser board).
It's all done on the cheap, using a chipped mirror (thanks, Mark for the help with optimizing the area to be masked out), looks even uglier in real life than in the photo, and there is nothing particularly innovative in the scope, but I am happy with it.
Travel-wise, I still need to make a cover for the mirror box and for the ventilation holes, and find a nice way of storing the secondary cell in the mirror box.
It's a total of about 16.5 lbs. The mirror box, which is about half of the weight, fits in my backpack and can be carry-on. Everything else is designed to go flat (the light shield, though, needs a better attachment than duct tape) and can just go along with clothes in a suitcase. The 32" strut comes apart into two sections which screw together, as the suitcase is only about 20" long.
Assembly requires one Phillips screwdriver (if I used knobs on the UTA, it would add to the imbalance, so I had to use screws there, and I also used them for joining the strut together). All the nuts for the Phillips screws are epoxied in place, while the other connections (including collimation bolts) are carriage bolts and three-lobe wingnuts with fender washers.
Except for the strut, all the wood is from my scrap pile. The mirror box and cell are some very tough 3/4" hardwood, probably oak. The strut is 1" square poplar, and is surprisingly very stiff, especially for something that is in two sections. Most everything else is (ugh) particle board ranging from 3/8 to 3/4". There are big ventilation holes in the mirror box as I want to use the scope in snowy Canada in January. The focuser is a push-pull Crayford, that needs some work to eliminate some wobble, but otherwise works fine. The az bearing is teflon on 12" vinyl record, and the alt bearings are teflon on painted particle board (works well enough--I expect eventually the paint will wear off and it'll be time to put on some laminate).
To get balance with the very small rocker board, I use springs. This isn't ideal, but it works.
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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
Edited by arpruss (10/29/09 12:18 AM)
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mark cowan
Vendor (Obsidian Optics)
Reged: 06/03/05
Posts: 2159
Loc: salem, OR
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Hmm, yeah, I'm not sure you're allowed to actually use duct tape in a finished scope unless your initials are R.G. 
Best,
Mark
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scopemankit
super member
Reged: 01/27/09
Posts: 142
Loc: south africa
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Nice to see a minimalist scope. Well done!
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Chris
Cape Town
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jayscheuerle
Post Laureate
Reged: 01/16/06
Posts: 4076
Loc: S. Philadelphia, PA
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Nice job! I was working on a similar design at one point for a 4.5" f/8, but it was too long to work out. One thing you might want to consider for simplicity/weight reasons is simplifying the light shield opposite the focuser. If you attach it directly behind the secondary, it can be much smaller. Yes, you'll have more diffracted energy, but it will be 90° from your spider support and may create a more aesthetically balanced + shape instead of a -. - j
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Fight indignorance!
The Green Goblin - 12" of dobsonian excellence!
The PortaBowl-a $100 4.5" f/8 ball-scope YOU can build!
Eero2-a 6" f/5 ball-scope you probably can't. 
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magic612
professor emeritus
Reged: 09/30/08
Posts: 561
Loc: Somewhere south of Chicago, IL
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If you don't go with the light shield idea of Jay's, you could always try using the adhesive-backed Velcro available at most craft stores. Apply that to the right material (or better yet, have someone sew on the non-adhesive type), and you'd be in good shape to slap it on quick and easy with no duct tape goo to contend with.
And by the way, I don't think it's ugly. I find its simplicity to be rather elegant.
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- Celestron C8+, Orion 90mm f/10, Orion ST-80, 5" f/8 Dob, 127mm f/9.4 refractor, 114mm f/8 on DS GoTo, 60mm Sears 6333-A, 127mm f4.4 refractor lens (current project), 12" f/5 mirror (future project)
- Orion Vista 10x50s (5 deg), Sears #6207 7x35 (7 deg), Jason #138 Statesman 7x35 (11.5 deg)
Yes, I'm addicted to telescopes and binoculars. I am getting help. Every time I look at the heavens, it helps.
http://www.eyesonthesky.com
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arpruss
scholastic sledgehammer
Reged: 05/23/08
Posts: 858
Loc: Waco, TX
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Thanks for the kind words. Some of the ugliness requires looking more closely to see.
I can't get myself to put another thing in the light path. I already have a 1/4" threaded rod, a largish 1.85" diagonal, and, above all, a 3.5" diameter semicircle covering up the part of the mirror where the figure is shot due to a chip (fortunately, a goodly part of the threaded rod is over the semicircle).
I've thought about velcro, but the loop is a coathanger (with the hook fitting into a hole in the strut--it's surprisingly stable) and the amount of velcro one could attach to a coathanger wire won't hold much.
I just had an easy idea: punch holes in the edge of the shield and use wire ties.
The alternative that I am also considering is to use a pop-up mesh basket (like a pop-up laundry hamper, but smaller), with foam on one side. I don't know if that would be lighter than my present arrangement.
By the way, initially I was thinking of four struts, but I decided to see if two were enough. I made it with two, and then found that it worked even better (i.e., better balance, and stability just fine) if I only assembled one in. Four would have been real overkill. The strut is solid enough that I feel good about picking up the scope by it. I can carry the scope with one hand, and the rocker and eyepiece case with the other, and that's great.
--------------------
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
Edited by arpruss (10/29/09 01:04 PM)
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magic612
professor emeritus
Reged: 09/30/08
Posts: 561
Loc: Somewhere south of Chicago, IL
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Quote:
I've thought about velcro, but the loop is a coathanger (with the hook fitting into a hole in the strut--it's surprisingly stable) and the amount of velcro one could attach to a coathanger wire won't hold much.
Well, I meant put ALL the Velcro on the fabric itself, not on the wire. Just fold it over the wire, and Velcro it to itself - Voila!
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- Celestron C8+, Orion 90mm f/10, Orion ST-80, 5" f/8 Dob, 127mm f/9.4 refractor, 114mm f/8 on DS GoTo, 60mm Sears 6333-A, 127mm f4.4 refractor lens (current project), 12" f/5 mirror (future project)
- Orion Vista 10x50s (5 deg), Sears #6207 7x35 (7 deg), Jason #138 Statesman 7x35 (11.5 deg)
Yes, I'm addicted to telescopes and binoculars. I am getting help. Every time I look at the heavens, it helps.
http://www.eyesonthesky.com
Edited by magic612 (10/29/09 02:04 PM)
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arpruss
scholastic sledgehammer
Reged: 05/23/08
Posts: 858
Loc: Waco, TX
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Quote:
Well, I meant put ALL the Velcro on the fabric itself, not on the wire. Just fold it over the wire, and Velcro it to itself - Voila!
Ah! Currently I am using a rigid foam sheet, but I could still make Velcro loops, though they wouldn't be as tight as wire ties.
If I used cloth, I'd have to make some sort of a wire frame for it to keep it rigid. It might still be lighter than the foam sheet, but not by much.
--------------------
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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magic612
professor emeritus
Reged: 09/30/08
Posts: 561
Loc: Somewhere south of Chicago, IL
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Hmmm... maybe paper clip the foam sheet to the coat hangar wire? Easy solution, would keep it in place, and paper clips are widely available if you lost them.
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- Celestron C8+, Orion 90mm f/10, Orion ST-80, 5" f/8 Dob, 127mm f/9.4 refractor, 114mm f/8 on DS GoTo, 60mm Sears 6333-A, 127mm f4.4 refractor lens (current project), 12" f/5 mirror (future project)
- Orion Vista 10x50s (5 deg), Sears #6207 7x35 (7 deg), Jason #138 Statesman 7x35 (11.5 deg)
Yes, I'm addicted to telescopes and binoculars. I am getting help. Every time I look at the heavens, it helps.
http://www.eyesonthesky.com
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arpruss
scholastic sledgehammer
Reged: 05/23/08
Posts: 858
Loc: Waco, TX
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Did wire ties. If I lose them, bit of string, floss or rubber bands will do just as well.
--------------------
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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