Picture of Homemade 12.5 inch Dobsonian Telescope

How to build a 12.5 inch closed tube Dobsonian telescope. I began building it in the spring of 2008, but the bulk of the work was done in July of 2008 with first light occurring on July 25. This Instructable describe the planning, design, and parts of the scope, as well as the process of building The scope. This is the first telescope that I have built

I found out pretty quickly that building my own telescope would only be a bargain if I made my own mirror and mechanical parts. This might have been tempting if I wanted to build a 6 inch scope—at that size, they say that first-timers do pretty well at grinding and figuring their own optics. But I wanted a larger mirror, and, at that size, grinding my own was not an option. I also wanted to buy the other mechanical parts—mirror cell, spider, secondary holder, and focuser—so that the performance of these pieces was not limited by my skills. When I looked at the costs, I seriously considered buying an Orion telescope instead of building my own. It would cost less and they have a very good reputation. But by this time I had thought about building my own scope for several weeks, and getting one off the shelf seemed pretty boring by comparison!


Once I decided to build a scope myself I had to decide on the aperture of the scope. 10 inch or 12 inch. For a while I decided that 10 inch would be the best size. Many sources point out that 10 inches is a kind of sweet spot in the balance between power and portability. A 10 inch scope would not be very much longer or heavier than my 6 inch, yet it would allow me to see much more. Yet I was also becoming infected with aperture fever. I had the thought that as long as I was going to build it I should build it as big as I could afford. The wood would cost the same, as would pretty much everything except the mirror, so why not spend a little more on the mirror and go BIG.


I was finishing this inner debate when I got a copy of the book “The Dobsonian Telescope” by Kriege and Berry as a Christmas gift. This book describes in great detail the steps to build a large aperture truss tube dob, focusing on scopes with a 12.5 to 40 inch mirror. It had been described by many as the most important recent volume for anyone planning to build a dob, and I have to agree. As I read the book I decided that I should build a 12.5 inch truss tube scope. As the authors describe the benefits of a truss design, it is hard to dispute their arguments. I even began taking careful notes about needed supplies and plans for each piece of the truss tube scope. As I continued to read, however, I was struck by the many complications of the design and, frankly, how many ways I could screw it up. The last chapter of the book describes a plan for an 8 inch sonotube dob with a few design elements from their truss design, and, as I read that chapter, the simplicity of its construction was very appealing. I decided that my best option was to scale up their 8 inch design for a 12.5 inch scope and sacrifice the portability and easier storage of a truss scope for something that I felt confident in building myself.

sky7771 year ago

Hi man

Its Nice but I think It's too heavy

Un-real!!! Nice work... and great instructable!
d1ndian2 years ago
Not worth the effort, price is tooo high.
maewert4 years ago
Very nice build nikon20. 

My first telescope I built was a 10" F8.  I wanted the long focal length for good contrast.  You really need a step ladder even for my 10" when pointed overhead.  I ground and figured the mirror with little troubles, making my focault tester, etc.  I wanted to finish that instructable before the contest ended but was too late :-).  I'd be willing to bet that you could easily grind your own 12.5 inch next time and save some $$.

The Dob is really a great design.  Perfect for visual observations with very heavy mirrors.  One 6in dob I made was a complete failure.  A 6 in primary mirror does not have enough weight to make the dob stable.  Funny how the bigger they are the better for dobs.

Thanks again for the 'ible.

Best Wishes
nikon20 (author)  maewert4 years ago
Thanks for the great comment. Im sorry to hear you couldn't make the contest. If you enter it in the next contest please let me know and i will make sure to vote for you. I would love to see your build when you are finished with it .
TCSC474 years ago
Thanks for your article. Nice looking telescope. A bit of a monster!

It has reminded me of one of my long term aims to make a telescope that has been buried by the demands of the rest of my life!

Rock on!
nikon20 (author)  TCSC474 years ago
thank you i am glad you like it
nikon20 (author) 4 years ago
After much debit and doubt i have taken the photos down cause i cannot be 100% sure that they were taking from my scope as i was not there to verify them and i do not want my contest entry to be based on photos and not the build process
urtlesquirt4 years ago
looks a lot like the limelight from MAKE Magazine.
nikon20 (author)  urtlesquirt4 years ago
that's funny it does i like the metal body it has i think that would be awesome to have
darrellb4 years ago
I'm glad I built my 10" truss dob before I read this 'ible! If I had known what I was getting into beforehand I would have choked! Ignorance is bliss! I received as a gift a 10" f/9 mirror that was ground in one of John Dobson's classes, and has proven very capable for the application. If I remake the scope there are some significant changes I would incorporate, but I love what I can see, and the truss design makes it light enough to be portable. Thanks for posting this and validating my work!
nikon20 (author)  darrellb4 years ago
your very welcome.
brobosky4 years ago
What a cool project.
If you could get by with 12" Sonotubes instead of the 14" you might be able to get them for free from large printing company or a local Paper converter. Most printers and converters have hundreds of 3, 5. 6, and 12 inch tubes they need to dispose of.
I work for a paper converter in Dallas and I would be happy to give tubes to a telescope builder.
nikon20 (author)  brobosky4 years ago
it sure would be easier to find than mine did but you wouldn't have a 12.5 inch mirror you would have to get a 10 inch mirror but astronomers say that is the sweet spot for telescopes it makes them easier to transport and you can still get the deep sky range if i ever build another it will probably be a 10 inch f6
eu334 years ago
Good build but its too big of a wall of text. You could have thrown in some paragraphs or any other text formatting.

It gave me an eyesore when i got to this step (4) and wasn't able to continue reading.

Good build indeed but watch the formatting so it would be more user-friendly.

Cheers !
nikon20 (author) 4 years ago
Thank you for all the comments and questions and ideas. Please don't forget to vote. When i get a chance ill post a instructable for a smaller scope that i helped make for my friends daughter.
kmpres4 years ago
Excellent project! Terrific detail and well written. I would love to build one but I don't have a yard large enough to accommodate even a small telescope. It will have to wait for my next house, alas.

Since it's now 3 years since you built it, do you have any pictures you can show us?  A video of how to set it up for observing a specific nebula would also be most welcome.

nikon20 (author)  kmpres4 years ago
I don't have a camera mount for it yet so i have no pictures with it as soon as i get a chance ill make a mount for it and take some pictures and video with it. It will have to wait till i get home though i am traveling for work and i am in the middle of planing a retractable roof building for it i always wanted a personal observatory lol
9ale74 years ago
hi, well done project, is it finished or not?
i didn't see any picture taken "from the telescope"??
can you take a picture of the moon ( or any other objects) and post it ( without cropping) and take a picture with regular DSLR or any digital camera?? for comparing.

nikon20 (author)  9ale74 years ago
yes it was finished in july 2008

I don't have a camera mount for it yet so i have no pictures with it as soon as i get a chance ill make a mount for it and take some pictures and video with it. It will have to wait till i get home though i am traveling for work and i am in the middle of planing a retractable roof building for it i always wanted a personal observatory lol
woodeye4 years ago
Thank you very much for posting this. A well written article.
nikon20 (author)  woodeye4 years ago
thank you
woodNfish4 years ago
What is the odd looking device on the tube above your focuser?
nikon20 (author)  woodNfish4 years ago
telrad Telescope Reflex Sight and a finder scope
master TELR001.jpgfinderscope.jpg
Nope. Sorry, MY mistake. I somehow didn't add in the mirror!
Details, details.... Sweet project! Something I have fantasized over for 40 yrs!
nikon20 (author)  burnerjack014 years ago
it sure was fun to make and use i am currently designing a more permanent base for it i always wanted a observatory lol
Please check your expediture math as there seems to be a glaring error of addition or omission of parts purchaced.
nikon20 (author)  burnerjack014 years ago
thank you for the info it seems to be working fine but i will recheck it
This is great and I'm sure you're proud of yourself! My father was an amateur astronomer and once attended a mirror grinding workshop led by John Dobson. Afterwards he had a video for sale that laid out how to build a Dob almost completely from scratch - grinding the mirror from an inch thick surplus porthole and finding the focal point off the faint reflection form the clear glass, then having it aluminized (I think this was the only non-DIY part). He also broke down how to fab an eyepiece holder and focuser. I wish I knew what the video title was! John is a kind man and an eccentric genius, even now at 96 yrs old! I treasure the pic I have of him and my father. Thanks for bringing back some nice memories :)
nikon20 (author)  PushTheOtherButton4 years ago
Thank you for the kind words i am glad this brought you back good memories and hope it dose justice to the work your father did
ChrysN4 years ago
Awesome project!
nikon20 (author)  ChrysN4 years ago
thank you it sure was fun to make