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Constructing a Dobsonian telescope at home.

  • Tianman
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Hi. Myself and my father are currently attempting to construct a 16" Dobsonian telescope ourselves. We are both new to this and have no experience constructing equipment like this. Has anyone else attempted to construct a Dobsonian or other telescope? I am having difficulty acquiring glass thick enough to make the parabolic mirror. Anywhere in Ireland seems to have a maximum thickness of 19mm glass (about 3/4"). Im not sure this is thick enough to prevent thermal expansion in a 16" mirror but I will probably settle for it as I am impatient and excited to get the project off the ground. If you have constructed your own, is there any advice you can give on things you would have done differently had you known from the start? Did you run into any snags along the way,or any advice at all would be helpful and appreciated.

thanks!
9 years 4 months ago #96302

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There are several people on these boards who have either built or restored telescopes, and I'm sure they will make themselves known. First I would say well done for considering this project
There is a lot of help also on "Stargazers Lounge" a British web site that operates like IFAS - but with a lot more members, I know they have a comprehensive site for telescope making
I would also say, you should also consider buying the primary, secondary and focuser and this could save you a lot of time. Polishing a mirror to the exacting standards needed (although possible) is a potentially long process after which you will still need to send it out of the country to have it coated!......everything is possible but wait for other comments and advice from more experienced members with more brain smarts than me

Declan

PS the glass in my own 16" is approximately 40mm thick
Last edit: 9 years 4 months ago by dmolloy.
9 years 4 months ago #96303

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Replied by michaeloconnell on topic Re: Constructing a Dobsonian telescope at home.

Tianman,

I previously built a 16" donb.
See this long thread:
www.irishastronomy.org/index.php?option=...2&id=48685&Itemid=40

Have a read of that thread and if you have any questions, just ask.

Photos can be seen in this powerpoint file here - a talk I gave a few years ago:
www.astroshot.com/Dob/dob.ppt

Michael.
9 years 4 months ago #96314

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dmolloy:There is a lot of help also on "Stargazers Lounge" a British web site that operates like IFAS - but with a lot more members, I know they have a comprehensive site for telescope making
I would also say, you should also consider buying the primary, secondary and focuser and this could save you a lot of time. Polishing a mirror to the exacting standards needed (although possible) is a potentially long process after which you will still need to send it out of the country to have it coated!


Thanks for the faith dmolloy! Stargazers lounge, Has that got anything to do with the Darragh O'Brien and Dr. Brian Cox show "Star Gazers?" Amazing show, it was on tonight and last night. I cant wait for the James Webb telescope to give some extremely deep field images of the edge of the observable universe! Sorry, I went off topic a bit there.Yes I will definately buy the secondary mirror and focuser. I cannot afford a new primary mirror as I am a recent graduate scientist and still unemployed : angry: . I assumed I could aluminize the reflective surface of the mirror myself? thanks for the help. I've contacted a lot of places and still had no help finding thick glass to use as a blank for the primary mirror.
9 years 4 months ago #96315

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michaeloconnell: Tianman,

I previously built a 16" donb.
See this long thread:
www.irishastronomy.org/index.php?option=...=48685&Itemid=40

Have a read of that thread and if you have any questions, just ask.

Photos can be seen in this powerpoint file here - a talk I gave a few years ago:
www.astroshot.com/Dob/dob.ppt

Michael


This is fantastic. I can see myself referring back to your information repeatedly over the construction process. I didnt get through it all as there is so much information there. The powerpoint presentation is brilliant. You have actually changed the picture that i have in my head of what my telliscope will look like. I'm keeping the file on my desktop for reference. thanks a million.
9 years 4 months ago #96316

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Actually Michael, I have a question. If you don't mind me asking, Where did you get that extremely impressive looking 16" mirror in the fancy suitcase? And how much did it set you back?
9 years 4 months ago #96317

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Replied by michaeloconnell on topic Re: Constructing a Dobsonian telescope at home.

I bought a mirror set from Telescope Service in Germany.
www.teleskop-express.de/shop/index.php
At the time, they had a 16" primary + secondary + spider for sale for about €1,100 IIRC.
It would be worth sending them an email and see if they still sell the 16" mirror sets.

As for the case, I got that custom made by a company called Consort Cases in Kilkenny.
Can't remember for sure how much it cost - think it was in the region of a little under €100.
www.consortcases.ie/
Last edit: 9 years 4 months ago by michaeloconnell.
9 years 4 months ago #96318

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Wow, they certainly don't come cheap. Although a 16" primary, secondary and spider for 1,100 it was a steal. Looks like I'll definitely be making my own though. I'm having a lot of trouble finding somewhere in Ireland that supplies glass thicker than 19mm.
9 years 4 months ago #96331

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Replied by michaeloconnell on topic Re: Constructing a Dobsonian telescope at home.

I wouldn't expect that you could buy such a thing in this country.
The cost of optics has fallen significantly in recent years thanks to the Chinese, making mirror gringing a dying art.
Perhaps give these people an e-mail:
www.galvoptics.fsnet.co.uk/telescope3.htm
Last edit: 9 years 4 months ago by michaeloconnell.
9 years 4 months ago #96346

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Replied by TrevorDurity on topic Re: Constructing a Dobsonian telescope at home.

Hi Tianman, might be worth giving Oldham Optics a shout as well. Their prices are high on their website but I picked up a used slower 12.5" from them for £400 a few years ago - F6. Though I guess at 16" the scope would be long! The prices quoted on the site are for 1/10 λ but they do quote for 1/4 λ on request.

www.oldham-optical.co.uk/

Surprisingly the part I found hardest to source when building was aluminium tubing - though I think that should be easier now.

Trevor
9 years 4 months ago #96354

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Replied by cathalferris on topic Re: Constructing a Dobsonian telescope at home.

Advice I've seen a number of times regarding grinding your own:
If you have never ground a mirror before and want to grind a larger mirror, grind a 6" or 8" mirror before starting the bigger mirror. The things that you learn with the smaller mirror will mean that the total time for the two mirrors will be less than if you were to start with the bigger mirror and making the same mistakes on the larger scale.

In general at the moment, it will be much cheaper to purchase finished optics than it would to grind a mirror of this size, especially when taking the cost of your own time and labour into account. It's only with larger mirrors that it becomes cost effective these days to grind your own, but the difficulties of grinding by hand are that much more difficult with the bigger blanks.
If being able to say that you made the mirror yourself is important then by all means go ahead and grind. Personally, I'd take a long and detailed look at sourcing the completed optics and then building the dob as per Kreige's bible and other links for books here:
www.cloudynights.com/ubbthreads/showflat.php/Number/5252285

Texerau's telescope building book has got a very good section on mirror grinding and testing, and is still current for that 50 years later.

(and I wish I had the time to do this myself..)
--
It's my madness that keeps me sane
Last edit: 9 years 4 months ago by cathalferris. Reason: Texerau's book reference / download
9 years 4 months ago #96357

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It might also be worth keeping an eye on astro buy & sell as I've seen a couple of examples of used optics for sale.

Perhaps a wanted advert?
9 years 4 months ago #96373

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