Large Aperture Collapsable Telescope

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Project by bbasiaga posted 12-14-2012 03:37 AM 3155 views 13 times favorited 25 comments Add to Favorites Watch

I built this telescope over the course of about 2 years. I started in 2009 by ordering the 22” mirror, which would take 12 months to get. In the mean time, I worked on the design and then started cutting wood.

The primary structures are made of Baltic Birch plywood. Some half inch, some three quarters, and most of the joinery is dowels and biscuits. The uprights and focuser board (red colored) are made of paduk. The basis for the design is John Dobson’s ‘Dobsonian’ namesake telescope. However I strayed from the basic design which has considerable size and weight for a scope of this aperture. The way the Dobsonian telescope works, in short, is like a giant teeter totter. The heavy mirror is supported on a frame inside the ‘mirror box’. The lighter ‘upper cage’ holds the eyepiece and focuser, and these two are connected by truss poles. You can see this in the second photo.

In the traditional design, the mirror box is built deep enough that its top corresponds to the center of balance of the mirror box and upper cage. Two smaller, semicircular bearings are permanently placed there to act as a pivot point to allow the scope to be pointed up and down. This whole assembly (mirror box, bearings, trusses, upper cage) then sit in a ‘rocker box’ which has the bearings’ mating surface. The rocker is bolted at its center to the ground plate, which then allows it to spin in azimuth. Thus, you can rotate the cage up and down on the bearings, and left and right on the rocker box.

In my design, which like many good designs is compiled from concepts seen in others’ designs, the mirror box is made just large enough to contain the mirror, its mount, and the mounts for the truss poles. Since the mirror box is not tall enough to reach the center of gravity, the bearings become much larger so that the center of the circle they would form reaches the scope’s pivot point, and still allows the scope to function. These bearings are almost 42” in diameter. To make this scope manageable, the bearings were made removable, and the rocker box was sized such that the mirror box could nest in it. With this design, the heaviest component is still manageable by my wife and I, and the scope itself collapses in to a small space. In the last two photos you can see it is actually possible to fit this monster in the trunk and back seat of a mid-sized sedan. Though honestly, we always just load it in our SUV.

Its a unique design and it has allowed us to have the power of a large aperture telescope available to us at home. I hope you enjoy!

-- Part of engineering is to know when to put your calculator down and pick up your tools.

25 comments so far

View waho6o9's profile


8785 posts in 3111 days

#1 posted 12-14-2012 03:50 AM

Amazing, thanks for posting.

View dustysawyer's profile


113 posts in 3163 days

#2 posted 12-14-2012 04:17 AM

Can a camera be incorporated into your scope? If so, you must do a follow up post and share some pics.

View BTimmons's profile


2303 posts in 3019 days

#3 posted 12-14-2012 04:27 AM

22 inches! Wow. My 10 inch Dob pales in comparison.

(Kneeling) I’m not worthy…I’m not worthy…

-- Brian Timmons -

View bonobo's profile


297 posts in 2591 days

#4 posted 12-14-2012 04:35 AM

My 6’ homemade dobsonian will barely fit in my trunk. I’m going to re-think my design along thes lines. Beautiful piece of equipment. How long does it take to cool down for enough for good viewing?

-- “The easy confidence with which I know another man's religion is folly teaches me to suspect that my own is also.” ― Mark Twain

View Cosmicsniper's profile


2202 posts in 3693 days

#5 posted 12-14-2012 04:41 AM

@Bbasiaga – That’s what I’m talking about! You won any ATM competitions at the major star parties yet? That’s just a beautiful design, well executed! I will be building my own at some point.

@Dusty – you could put a camera where you mount the eyepiece, and some people use web cams to take some of the worlds most incredible planetary images. For deep space objects, in general, you need a way to track the scope to keep up with the earth’s rotation. You can put dobs on tracking platforms to help in that regard, but images will still suffer something called field rotation. Unless you are content with short exposures (perhaps a minute at most) of brighter objects, you’d need a polar-equatorial mount, like one shown in my avatar. The dob is alt-az (altitude-azimuth).

-- jay,

View Monte Pittman's profile

Monte Pittman

30458 posts in 2872 days

#6 posted 12-14-2012 05:11 AM

Welcome to LJ’s

This is really impressive

-- Nature created it, I just assemble it.

View a1Jim's profile


117742 posts in 4111 days

#7 posted 12-14-2012 05:14 AM

A very cool telescope great job.

View Matt Nudi's profile

Matt Nudi

121 posts in 2525 days

#8 posted 12-14-2012 05:21 AM

Wow this is amazing, I could see making something like this later in life. Have fun with it

-- - Still a new guy to the craft, but always striving to learn more

View davidroberts's profile


1027 posts in 4020 days

#9 posted 12-14-2012 06:21 AM

I love telescope builds. I had my old 13.1” Coulter reground and recoated. Threw away all the other particle board base and sonotube (haha), kept the secondary and focuser. Basically I’m down to glass. You did a fantastic job. I’ll probably steal parts of your design, some day. If you don’t mind, who ground your primary, and what is the stop. I think my Coulter is 4.5. Toss in a couple of three Naglers and a paracore, and you’re good to go. I would be too., and also broke!

-- Better woodworking through old hand tools.

View redryder's profile


2393 posts in 3636 days

#10 posted 12-14-2012 07:10 AM

Nice photos.
I haven’t even made a bandsaw box yet….................

-- mike...............

View deon's profile


2522 posts in 3560 days

#11 posted 12-14-2012 07:43 AM

Enviable wow!

-- Dreaming patterns

View Doe's profile


1428 posts in 3364 days

#12 posted 12-14-2012 09:07 AM

Wow! I envy you. I’d like to see a couple of pictures as well.
(I think so, Brain, but where will we find a duck and a hose at this hour?)

-- Mother Nature talks, I try to listen

View stefang's profile


16803 posts in 3868 days

#13 posted 12-14-2012 11:22 AM

Congratulations on a great design and build. I hope you will include some photos from it with your posts.

-- Mike, an American living in Norway.

View bbasiaga's profile


1243 posts in 2529 days

#14 posted 12-14-2012 01:27 PM

Thanks for all the kind comments. To answer a few of the questions:

- As stated a camera can be placed where the eyepiece goes, but this scope is not motorized and that severely limits photographic opportunities. Even with a very wide eyepiece, or no eypeice at all, the FOV is quite small and the objects move quickly through it due to the sideral motion of the earth.

- I keep in in the garage so it is firecracker hot in the summer, but not much warmer than ambient in the cooler weather. In summer I like to let it sit outside for 2-3hrs before dark, and by midnight its pretty well equilibrated. The short mirror box doesn’t hold much air which both helps equilibrate the scope faster, and makes it more susceptible to dew (always trade offs), but the truss cover does an excellent job with the dew. On its first-light voyage, i could literall write my name in the dew on the top of the mirror box, but the mirror stayed clear.

- The mirror was figured by Steve Swayze, and it is an F/4. It still requires a 4’ -6’ ladder to view high overhead. You only need to be 2-3 steps up (well, I only need to be 1 -2 steps but I’m tall. My wife…not so much)

- I have not won any ATM contests. I have not entered any either. I have had it to Nebraska Star Party and many of our local club’s parties. It is always a popular view. There is a guy in our club with a 24” though. Traditional Starmaster. He has to have a small trailer to haul his around.

Any ATMs out there who want to know more, post here or PM me.

-- Part of engineering is to know when to put your calculator down and pick up your tools.

View BigMig's profile


473 posts in 3148 days

#15 posted 12-14-2012 02:56 PM

Dude – it’s great to see another woodworking LJ-er. Your scope looks fantastic. Where do you observe from? Swayze mirror – you can’t go wrong there. I may be observing tonight – catching a few late Geminid meteors. Hope you can do the same.

Please keep posting!

-- Mike from Lansdowne, PA

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