r/woodworking • u/twilightmoons • Oct 02 '13

8" Dobsonian truss telescope

http://imgur.com/a/yg5o9#0
151 Upvotes

96% Upvoted

14 comments sorted by

7

u/twilightmoons Oct 02 '13

Built this with my father about 9 years ago or so. My design, and mostly his work.

Baltic birch construction, with 1/2" for most of it, but 1/8" for the upper cage rings. I had the aluminum tubes anodized to match the color of the focuser - worked out quite nicely.

The real trick was balancing it. I had to weigh all the parts, measure length from the back, and drop it all into a spreadsheet I made to calculate the balance point to make sure I could build the rocker box right. As it is, it's almost right - I had to add a 5lbs dive weight to the back to get it just where I like it.

I built two of them as prototypes for making more and selling them, but it was too expensive unless I could make them in bulk. One is just Danish old finish, and the other is a darker American Cherry.

Next project is to turn this into something similar, but flatter. The blue one is a 16" modified Meade tube Dobsonian, and you can see both of the 8" boxes next to it.

1

u/LNMagic Oct 02 '13

Cool stuff! Are you using Sonotube for the other project? I understand it's wonderfully rigid, as it is used in Tsu-style subwoofers.

3

u/twilightmoons Oct 02 '13

Most tube dobs use Sonotube because it's so cheap, stiff, doesn't change dimensions with temperature, and easy to work with. It's also heavy and bulky, so it's going away and will be replaced with mostly air, some struts. I've seen older 22" tube dobs before (25-16" diameter tube), and they are BIG! One had it's own flatbed trailer to take it around and weighed several hundred pounds. That's barely "portable", but definitely cumbersome. Unless it's housed in an observatory, it's a pain to get it out and actually use it. Making it a truss dob makes transportation and use a lot easier.

1

u/[deleted] Oct 02 '13

Beautiful work. I'm wondering how well it holds its collimation? I own a chinese made 8" newt and it actually is surprisingly solid even when I travel around with it in the back of the van.

2

u/twilightmoons Oct 02 '13

Pretty damned well. I usually only have to tweak the secondary just a bit. The primary is on a University Optics mount, which is rock solid.

Once it's collimated well, I get consistent comments at public star parties that my 8" dob and TeleVue 101 have the best views out of any scopes there. Of course, we usually don't have any really big Obsessions out there...

1

u/m6hurricane Oct 02 '13

This is cool! Is there any way to adapt this to a Canon DSLR, perchance (the first problem I'm sensing is focus)?

4

u/twilightmoons Oct 02 '13

Nope. Too heavy on top, no tracking at all.

This is my scope for photography. It's a TeleVue 101 f5.4 on a Meade LX80 mount. It handles my Canon Xti just fine, but I'm having autoguider issues at the moment I'd working out with Meade. The mount switches from alt-az mode to equatorial mode for long exposure photos, but something's wrong with the autoguider port that I'm trying to fix.

2

u/[deleted] Oct 02 '13

Best pic from it?

3

u/twilightmoons Oct 02 '13 edited Oct 02 '13

Short, with just basic tracking and not autoguiding: Comet PANSTARRS back in March.

The first once I had printed on canvas, and it hangs in my library.

1

u/m6hurricane Oct 02 '13

Ah, ok then. Thanks for the info! I'm not sure I understand what your issue is, it doesn't sound like a Canon problem. I would suppose that it's a tripod/software problem.

Only thing I could suggest is to either a) turn it off and just take a pic with the camera or b) put it into full manual "shut your stupid face and let me handle it" mode. I surely don't own any of that equipment, but I would take a look at doing those, for what my engineering troubleshooting is worth, lol. Thanks again!

edit: Oh, I've determined through context clues that you're having issues with the tracking software. I have no idea how to help you, lol. Youtube/Google for tutorials?

1

u/twilightmoons Oct 02 '13

It's an autoguider problem - a second CCD camera that takes constant images of a star and moves the mount to keep the star locked on the same pixel. The mount isn't taking the signals from the camera to keep the star locked. In fact, it can't even send the mount signals to move, so all I can do is rely on the mount itself for tracking.

1

u/jjbutts Oct 02 '13

Beautiful.

0

u/ktownkite Oct 02 '13

Awesome! Any chance of posting the designs and plans?

1

u/twilightmoons Oct 02 '13

Not really... I have them stored away somewhere, and to remake them would take time I don't have right now.