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.

Remove these adsRemove these ads by Signing Up
1-40 of 47Next »
sky7778 months 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.
maewert3 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)  maewert3 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 .
TCSC473 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)  TCSC473 years ago
thank you i am glad you like it
nikon20 (author) 3 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
nikon20 (author) 3 years ago
(removed by author or community request)
I call shenanigans on every picture in this post except for the the moon.

Please explain, in detail, how you attached your tube to the very unique drive system of an XT12G mount.

I would also like to know about how you can take such fantastic pictures without a field rotator and an autoguider system. Over how many nights did this photography session take place? Deep space photos like these require HOURS of exposure for each one.

Similar photos at require 100+ minute exposure times on his 20" telescope and $3200 camera.

Until I see photos of this scope setup for these pictures and an explanation of the exact equipment used, I cannot believe that these pictures were taken with this OTA.

Someone is pulling someone's leg here. Your astrophotographer friend may have included his own images from his setup.
nikon20 (author)  LVLaserTech3 years ago
Like i said these are not my photos and i cannot coment on exactly how he set it up as i was not there all i can say is i saw the mount he used when he picked up the telescope. All i did was supply the telescope as far as his camera equipment i dont know what he used i never saw it all i know is he had my scope for about a month while i was traveling and he gave me these photos. ill ask him for a detailed list of what he used and when i get that ill post it here for you.
There are a number of technical reasons why these photographs could not have come from this Optical Tube Assembly.

While I applaud your building of a homemade Dob, (giving you the FULL benefit of the doubt here) your "friend" has provided photographs that make it look like you're trying to win by cheating.

I have no dog in this hunt whatsoever, but if people are impressed by these photographs and vote for it because of them when there's no proof that this scope generated the photos and there IS data to the contrary (see below), then that's certainly not fair to the other contestants.

Here's a detailed response from a thread at CloudyNights:

"The image scale is wrong on the M31 image, fits too much of the galaxy in for even a 35mm chip. And you can tell it's not a mosaic because the stars at the corners show coma/field curvature artifacts. Also no obvious diffraction spikes in the m31 photo.

My guess is that photo was taken with a refractor. Another thing, the resolution on the Dumbell nebula seems a bit too high for that telescope.

Attached is CCD Calculator showing what the FOV on M31 would look like with that scope (assuming f/5... I didn't bother reading his whole article to figure out what f/# he used) I am not trying to say that good AP isn't possible with a sonotube scope,

(the 'friend' may very well have pulled it out of the dob mount, added rings and a dovetail, and mounted it on his CGE-Pro or comparable) but in this case it is unlikely."
nikon20 (author)  LVLaserTech3 years ago
LVLaserTech is right please do not vote for the pictures my instructable is for the build of the telescope not the quality of the photos.

and as i said before i was not there is there a possibility that he sent me the wrong photos sure is there a possibility that he used a different mount than the one i saw sure is there a possibility that he is lying to me me about what he did sure. I wasn't there so i can be 100% but i do not think my friend was lying to me and i believe the pictures are from my telescope my kids use it for stargazing a lot i have seen some deepspace but i use it mainly for sketching the moon and i like to view solar flares. On that note

do not look directly into the sun and never point a telescope into the sun without proper filtration you can damage your telescope and burn your retinas and possibly go blind

i am not a astrophotographer so i cant comment on the quality of the pictures since there is so much doubt on the photos i will gladly take them down. i am not trying to win this contest with photos. i got a email that someone built a telescope close to mine that has seen the stuff in the photos here is a link to his site

if i seem a bit rude please forgive me i just spent 12hrs in a plane i have jetlag and im sitting in a airport.

i would like to thank lvlasertech for keeping this instructable lively and informative.
I have seen some VERY impressive photos similar to those, taken with Nikon
D700 and D300 cameras, with the proper filters- and mounts- on a quality scope.
While I will freely admit that most astro-photography is WAY beyond me, you certainly do NOT need a $3200 camera to do so.
Some of the very best planetary and deep sky pics I have seen have come from a Fuji S3 professioanl camera [based on a Nikon body] and a Canon 20Da, which was designed with [I think...] a user replaceable inside the mirror box filter for astral photography. Both cameras have fairly small megapixels by todays' standards, and are certainly obsolete, but do the job extremely well!
Remember: It is the quality and SIZE of the capture chip, NOT the megapixels that determines quality.
A neet site:

Cool instructable, Dude!
he might just have a $3200 camera, they aren't very hard to come by
The last time I checked, that particular SBIG camera used on TelescopeGeek had an eight month lead time.

A 20" scope gathers 2.6 times more light than a 12.5" scope, therefore equivalent exposures on this one would take 200+ minutes, at least. An Altitude Azimuth mount would also require a field rotator.

There's no way these were taken with an Orion GoTo Mount.
nikon20 (author)  LVLaserTech3 years ago
that is a great website that guy has some fantastic photos
Stunning sir, absolutely stunning.
Are you referring to the photographs or the telescope itself?
nikon20 (author)  LVLaserTech3 years ago
the photographs
nikon20 (author)  The Ideanator3 years ago
thank you. I had to scale them down to fit in the post but the full size pictures are beautiful the objects are alot bigger and more vibrant and detailed.
what kind of drive did you use here? a Dobsonian is an alt-az mount, and not capable of time exposure tracking... and I am assuming that these are time exposures. Nice pics, and a nice build, btw.
nikon20 (author)  stringstretcher3 years ago
we had used a dobsonian goto mout from orion
urtlesquirt3 years ago
looks a lot like the limelight from MAKE Magazine.
nikon20 (author)  urtlesquirt3 years ago
that's funny it does i like the metal body it has i think that would be awesome to have
darrellb3 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)  darrellb3 years ago
your very welcome.
brobosky3 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)  brobosky3 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
eu333 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) 3 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.
kmpres3 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)  kmpres3 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
9ale73 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)  9ale73 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
woodeye3 years ago
Thank you very much for posting this. A well written article.
nikon20 (author)  woodeye3 years ago
thank you
woodNfish3 years ago
What is the odd looking device on the tube above your focuser?
nikon20 (author)  woodNfish3 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!
1-40 of 47Next »