Telescope Making

I built my 12.75-inch Dob for less than $700 — much less than a comparable commercially made scope would have cost. But is making your own scope always a money saving proposition? That's what inquireing minds (canine or otherwise) want to know.

For diehard ATMs, building telescopes is a way of life. But for others, the decision about whether or not to make a scope often hinges on economics. Will I save money building my own? The question shows up regularly in on-line forums and in my e-mail box. Before the emergence of a large-scale commercial telescope industry, the answer was a definite “yes!” But with the current abundance of low-cost, imported Dobs, and the increasing expense (and scarcity) of telescope-making supplies, it’s reasonable to wonder if it’s still possible to save a few bucks by going the home-made route. The prevailing conventional wisdom says “no,” but my own experiences suggest the answer isn’t as cut and dried as that.

Me, my new scope, and a bloody big rock. (Courtesy George Brandie)

My new airline-portable telescope is featured in the March 2013 issue of Sky&Telescope, but given the publication's finite page space, it wasn't possible to include a great number of photos. So, presented here are a series of detail images along with some construction tips and tricks. Keep in mind that this isn’t intended to be a full description of the scope and how it's built — it’s merely a supplement to the S&T article, so be sure to give that a read first.

Requiring only a few parts, this simple and effective setup provides stable images for detailed views of the night sky.

“This is the best binocular mount I’ve ever used!”

Those were the first words out of my mouth as I came indoors from testing my just-completed binocular rig. It’s rare that I build something that actually works better than expected, but finally I’d come up with a binocular mount that provides steady views, is easy to use, very portable, and simple to build. It was a good night.

I’ve been building and using telescopes for more than three decades and I’ll share with you a secret: collimating a Newtonian reflector is easy. So why does it seem so difficult when you’re just starting out? Probably because you’ve done your homework by Googling the subject and have read and re-read everything you’ve found. And now, you’re lost in a forest of information — some of it contradictory, some of it densely technical. Truly, sometimes less is more.

Any new telescope-making book is a big deal, but one that is both new and important is a huge deal. I believe that’s what we have here with the arrival of Albert Highe’s Portable Newtonian Telescopes. It’s a very satisfying, and detailed volume that covers a great deal of territory not explored in any other telescope-making book. What makes it "important," in my view, is that it not only advances the state of the art, but also provides a wealth of information that will stand the test of time. Albert, and his publisher Willmann-Bell, are to be congratulated on producing such a fine and valuable addition to the ATM's bookshelf.

This ultraportable telescope is ideal for outings in which stargazing is a “maybe” instead of a “definitely.”

Although I have a house full of telescopes, I still find myself dreaming up new ones that would be ideal for this or that situation. But that’s one of the real joys of learning to make telescopes — you can build instruments uniquely suited to a given application, limited only by your budget, skill, and imagination.

This image of the Scorpius Milky Way was captured from Costa Rica with a DSLR camera and the simple hinge tracker mount described here.

If you have a DSLR camera and are interested in astronomy, you’ve probably considered dipping a toe into the astrophotography waters. But a camera is only part of the equation — for exposures longer than a few seconds, a tracking mount is usually necessary. Unfortunately, most suitable mounts are relatively bulky, or expensive, or both. But not the hinge tracker. It costs less than $10 to build, takes less than an evening to assemble, and requires no batteries. And best of all, you can put one together even if you’ve never built anything more complicated than Ikea furniture.

There’s no getting around the fact that collimating your reflector telescope (Dobsonian or otherwise) is much easier when the centre of the primary mirror is marked with a paper doughnut. Thankfully, these days a good number of commercially made telescopes come with their mirrors pre-marked. But if your scope isn’t so equipped, don’t worry — the procedure for adding a centre doughnut isn’t difficult. In fact, the hardest part might be convincing yourself that you can take out the primary mirror without inviting disaster.

Aligning the optics of your reflector telescope is crucial for optimal performance — all the more so if you have a telescope with a focal ratio of f/5 or less. A good tool can make the difference between successful collimation, and an exercise in frustration that encourages you to settle for “good enough.” But selecting the right tool can be more confusing than actually using it. On-line discussions offer a bewildering array of opinions and experiences — some of which posted by people who make and sell the products they (naturally enough) recommend. So what do you really need to collimate your scope?

Although the internet can be a wonderful resource for first-time telescope makers, it can also be a source of great frustration. No matter what the topic, it’s possible to find completely contradictory advice. Far more dependable are good ol’ fashioned books — especially those that have stood the test of time.

Attention to detail is what separates a regular Newtonian reflector from one optimized for high-contrast performance. This 6-inch f/9 uses every trick in the ATM’s book to deliver superb planetary and deep-sky views.

This was the first telescope I made using my own optics. Like most telescope makers, I got started the easy way, by building Dobsonians with mirrors ground by others. But one day I got bit with the mirror-making bug. I blame my friend Lance Olkovick, our local club’s mirror-making ace. But why a long-focus 6-inch? At the time I was a hardcore Jupiter junkie and was convinced that a long-focus Newtonian would deliver excellent views of my favourite subject. I also wanted to prove a point.

The old saying that less is more rings true for telescope magnification, but there are many factors to consider before choosing your ultimate wide-field eyepiece.

Low-magnification views of the night sky can be breathtaking. It’s only with low power that we can fully appreciate the splendor of the Pleiades, the foggy expanse of the Andromeda Galaxy, or the wispy filaments of the Veil Nebula. But if discussions on internet forums are anything to go by, there's a lot of confusion out there about how magnification, field of view, and exit pupils relate to each other. And without understanding these factors, you might end up shortchanging your telescope’s low-power capabilities.

The Astroscan’s greatest strength is its bare-bones simplicity, which unfortunately also means it lacks adjustments for achieving optical alignment.

Edmund Scientific's Astroscan has been around since 1976. Its enduring appeal is at least partly due to its no-muss-no-fuss simplicity. You plop it down in its base, put in an eyepiece, and you’re good to go. The optics come factory aligned, so you never have to worry about collimation. Unless, that is, the mirrors go out of alignment. And since the Astroscan doesn’t have adjustments to correct this malady, you’re stuck. But are you really? For the brave (or, perhaps foolhardy), there is a procedure you can perform that will put the scope’s optics back into alignment.

My dear fiend Lance Olkovick (a.k.a. Nanook of the North) observing Jupiter at dawn from Mt. Kobau with his 12½-inch f/5. The scope I'm building will be similar to this.

The nights are cooling down and the days becoming increasingly overcast and grey. That can mean only one thing: it’s Telescope Making Season again. And so, I’ve decided to tackle a project I’ve had in mind for some time now, namely, a rebuild of my 12¾-inch truss Dobsonian.

Day 8: Going Round in Circles

Routing the hole for the top of the mirror box.

Cutting neat, tidy circles in plywood. This is where a plunge router really shines. And make no mistake — building a Dobsonian means cutting circles. In the case of my scope’s design, the first ones are for the tube ring and for the flange at the back of the tube, where it mates with the mirror box.

Day 15: Side Bearings

A finished pair of side bearings. The slots will serve as simple handles once attached to the mirror box.

Sometimes what seems like it should be a quick and easy operation, turns out to be unexpectedly complex. Making the side bearings from my scope was one such a case.

Day 22: Completing the Upper Tube

The scope’s upper tube all done. The gloss-black finish is achieved with Monokote.

With the mirror box done, it was time to move on to the comparatively straight forward job of finishing up the top half of the scope. This consisted of two tasks: giving the cardboard tube a protective covering and attaching all the hardware.

What you need to know when it comes to optimizing your scope’s thermal behavior.

Generations of backyard astronomers have debated why, inch-for-inch, the performance of a high quality refractor usually edges out an equal-quality Newtonian reflector. This disparity is most apparent when viewing low-contrast planetary detail — the images in a good refractors often have a touch more snap to them. Is there some intrinsic shortcoming in the design of the Newtonian reflector that makes this inevitable?

Solving the thermal management puzzle can be as simple as adding a fan to cool your telescope's primary mirror.

In Part 1 I described the cause and consequences of telescope thermals, now let’s see what can be done to cure, or minimize the problem.

The secondary mirror holder and spider on my 12¾-inch truss-tube Dobsonian is made with scrap wood, a few nuts and bolts, and a stainless-steel ruler.

The curved-vane secondary mirror holders I use on almost all my telescopes never fails to excite curiosity. Most people know that the principal benefit of the curved spider is spike-free stars, but they often wonder if it really works. The “points” adorning bright stars in telescopes with straight-vaned spiders are diffraction artifacts that don’t seriously affect the image but do impose an aesthetic quality that may not appeal to you. Luckily, the remedy is easy to make, works like a charm, and can be retrofitted to virtually any reflector — commercial or homemade.