August 23, 2014

Making a Newtonian Reflecting Telescope for less than 50$USD

Telescope.

Stove-pipe Telescope plus Lab! (All Photos by Author).

Most amateur astronomers harbor a secret passion to, at some point, build their own telescope. Constructing a telescope puts you in a select realm of Amateur Telescope Makers (ATMS), and gives you intimate knowledge of how telescopes and optics really work. Another plus is as with anything, be it a house or a scope, if you want features to your own exact specifications, your always best off to build it yourself. Mass produced equipment generally means compromise. And until about the 1950s (when the concept of mass producing everything first came in vogue), if you wanted your own telescope, you had to build it from scratch.
There is however, some debate as to weather it is still worth it financially to build your own scope. The advent of mass production has also meant that quality instruments can be had for as little as 200$. But what about the shoe string range, were most of us mortals reside? Can a quality telescope be constructed for under 100$?
I suddenly found an immediate reason to build my own instrument this summer; after retiring from the military, both of my telescopes were in storage. I found myself facing a scope-less future, with pristine night skies outside our camp on the shores of Saint Froid Lake in northern Maine. Buying yet another scope was out of the question; we had more pressing purchases at hand. I decided to resurrect a childhood idea of mine; to build a 6 inch Newtonian reflector out of a piece of stove pipe.
Now is the point I should make it clear concerning my limited engineering abilities. I’m not the sort of guy who will build a bathroom on the weekend. I worked with explosives in the military; I’m good at destroying things. If you want things to explode when they’re supposed to, I’m your guy; you might not want to let me under the hood of your Chevy. Still I wanted to build my own scope for… you guessed it… the experience. I always wanted to enter the elite world of the ATM. While others are drawn to the flashy scopes that cost a second mortgage at star parties, it’s always the “junk yard” scopes that have captivated me. To raise the bar a bit, I decided to use funds exclusively from bottle returns (see “Making your workouts pay”; http://astroguyz.com/?cat=1). These are not princely sums; therefore, I hoped to complete a Newtonian reflecting telescope for under 100$ USD. I selected the Newtonian design because of its simplicity; you have a concave primary mirror, plus a secondary that aims the light at the focus.
I was fully ready to experience the joy/sorrow of fabricating my own mirror. I knew from previous research that a 6 inch glass mirror blank cost about 60$. However, a quick search on Ebay revealed something startling; a 5 inch mirror kit for under 20$! It was a factory reject; the kit came with a f/8 primary, a 1-1/2″ elliptical secondary, and all the mountings. It states that the mirrors were rejected by Meade because they were “slightly blemished…” My own inspection out of the box reveals only slight scratches at the edge of the primary; otherwise, you would be hard pressed to figure a mirror to such exacting specs. Views do not “pop” like the UHC coatings on other factory Meades (the blemishing, perhaps?) but otherwise, the price was a steal. The dealer was scopehed1; definitely check them out! I still hope to grind my own mirror to gain those “skills” at a later date.
Let me also note at this point that I currently do no possess a work shop, and have only limited tools, power or otherwise. The assembly would be done with nothing more sophisticated than a hand drill and a pocket knife. It’s always been daunting for me to see these guys construct scopes that have access to their own personal fabrication shop; I promise, I used common tools. Maybe someday, I’ll have a drill press…
Next, to find a suitable tube. I was able to procure a piece of aluminum stove pipe for free from the local dump in Eagle Lake;

6? stove pipe.

I love the dump here in town; they don’t mind if you rummage through their junk! I had some reservations about the aluminum tube; I thought it might flex considerably. Also, the two joined sections were not straight and would need to be reinforced, and the ends were not flat. Any measurements for mountings would involve a certain amount of guess work. Still, when I placed the mirror cell in the tube, it fit… perfectly.
After cleaning the tube, the first order of business would be to measure for the drill holes to mount the primary, spider veins, focuser, handle, and finder. I definitely wanted to drill before any glass was mounted, to avoid damaging the optics. Some items like the handle and finder were purely preference; others, like the secondary mountings, were crucial. For the preliminary calculations, I used a site known as NEWTONIAN TELESCOPE DESIGN PLANNER (v/IE1.3) at http://www.catseyecollimation.com/designie5.html . This allows one to input the parameters of the telescope and outputs useful measurement values, albeit with some of my own modifications, owning to the irregularity of the cylinder used. I knew that an f/8 mirror would achieve focus at 8 x 5=40 inches; the key is to have the focuser and the secondary aligned to hit that sweet spot. (And again to do it with a hand drill!) Anyway, several bit changes and re-remeasurements later, the cuts were marked the one of the truly great inventions of the 20th century, post-it notes:

The naked scope.

Another image shows the precision methods used to complete the measurements;

Measurments for the secondary.

Note the high tech duct tape covering the sharp end of the tube. Any great project generally has some duct tape involved; I think it gives the scope a glossy, space age look. After all, duct tape was used in old b-movies as low tech uniform trim!
Next, to paint the tube. Again, this is done sans optics. A note; spray painting in sub-zero temperatures is less than optimal. It’ll take days to dry, and paint does freaky things at low temps. Again, that no work shop thing… but I digress. The next step is to mount the goods on the dried tube assembly. Then, we’ll see if our calculations were true. Below is a lay out of the attaching hardware;

Attaching hardware.

Two devices were of my own conception; the focuser and the finder. The focuser is simply two pieces of PVC mounted with small right angle braces; focusing is achieved by loosening a set screw and sliding the eyepiece. This is what’s known as a version of a helical focuser. I like the right angle braces because it enables me to “shim” washers in place to align the focuser tube with the secondary.

PVC helical focuser.

Note the dental floss crosshairs used to align the mirrors! Another innovation was the use of a laser pointer for a finder;

Laser pointer finder.

Certainly, mounting lasers on telescopes is nothing new, but perhaps my idea to use binder clips is!
Next, on to the mounting; often overlooked, this can make or break a scope; even the slightest amount of wobble can make a scope unusable. I used a configuration of band clamps, screws, and a wood block as shown;

Tripod adapter.

The block mates to the tripod head by means of a recessed nut hammered into the wood and screwed behind a metal plate. The tripod is a 10$ thrift store purchase that I’ve used for various applications over the years;

Tripod.

Now for the fun part; optics alignment. Actually, this was easier than I had feared. The mirrors came with the fine tuners installed so it was just a matter of practice to get them in rough alignment.

Mirror alignment.

Upon getting my scope out into the open air, however a major flaw was apparent; I was not able to achieve focus with a 26mm eyepiece! Doubtless, it was those “cylindrical irregularities” at work again; (see above pic!) a 1/2″ copper tubing as a spacer proved to be the solution.

Scope in alcove office.

All told, the scope cost $41.92! This includes;

Mirror kit: (including shipping) $29.95
PVC Helical Focuser: $2.33
Tripod mounting parts: $4.67
Handle: $4.97

I know, the total doesn’t include things I already had kicking around in my astronomy life, such as the eyepiece, tripod, and laser finder. The handle alone was a 5$ extravagance I purchased at Lowe’s that I probably could have scavenged for at the dump as well. And the laser pointer is more expensive than the entire rig! Still, I can think of several homemade 1x rigs that could be substituted. And, for cheap eyepieces, again, Ebay to the rescue.

Scope and snow.

So, you ask, how well does the completed product function? Well, at about 8lbs., the optical tube is probably at about at the limits of what the small tripod can handle. And the 5mw laser finder doesn’t like arctic temperatures much; I may upgrade to a telrad backup. (Ebay, anyone?) Still, images of the Moon and Venus have been sharp and crisp, and the optics star test well. The helical PVC focuser takes a bit of practice, but a washer super-glued on to the set screw (someday, a wielding torch!) makes it much easier to manipulate with gloves on. But best of all, I finally have my own homemade scope! Maybe I can show my face at Stellafane next year… it’s been a long time coming!

Comments

  1. hahah.. nice.. lol

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  3. [...] This post was mentioned on Twitter by MyschaTheriault, David Dickinson. David Dickinson said: http://bit.ly/aO3n7G Making a Newtonian Reflecting Telescope for less than $50; a classic Astroguyz post! [...]

  4. [...] you have to already know a bit about astronomy and observing equipment. If you do however, these homemade telescope instructions show you how to build your own for less than 50 USD.  Great for when your child has only begun to [...]

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