Telescope Making

With the final modifications completed, the scope is at last finished. At least for now...

The balance issue detailed on Day 23 was eating away at me, so I broke down and decided to make the necessary modifications after all. I’m glad I did. The work wasn’t as bad as I feared, and the results turned out better than I expected.

Requiring only a few parts, this simple and effective setup provides stable images.

In my Telescope Workshop column in the August 2010 issue of Sky&Telescope, I wrote about how you can build my newest (and best) binocular mount. Presented here are some additional photos to aid you in constructing one.

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.

This simple, easy-to-build mount provides the perfect introduction to long-exposure astrophotography.

Round stars. That’s the difference between astrophotos captured with a camera that tracks the sky’s motion versus one that doesn’t. Traditionally you’d make a tracked photo by placing your camera piggyback on a telescope with a motorized equatorial mount. But that’s a lot of equipment to deal with if all you want are some nice-looking constellation portraits or a shot of a newly discovered comet — especially if you have to travel to reach your favorite dark-sky destination.

Have scope, will travel! This Dobsonian not only gives great views, it also fits into an airplane’s overhead storage compartment.

One of the best reasons for learning to build telescopes is that you can make instruments that perfectly match a particular observing need or circumstance. As an editor at Sky & Telescope, my “circumstance” happily involved a lot of travel, and as a result I found myself dreaming of a telescope that I could take with me as I zig-zagged across North America from one star party to the next. It seemed a shame to arrive under the dark skies of the Texas Star Party or Mount Kobau without a telescope of my own.

With star-party season upon us once again, you're probably confronting the age-old problem of how to protect your prized telescope from the triple threat of dust, rain, and heat. The traditional big, ugly trash bag or blue tarp works for two of those three (dust and rain), but looks bad and lets your scope to get way too toasty on a hot summer’s day. Alternatively, you can plunk down $50 or so on a proper dust cover, but if you’re like me, that cash almost always seems to go towards another eyepiece instead. Stumped? Don’t worry — a cheap, effective telescope cover is only as far away as your local hardware/camping-supply store.

Remounting your Newtonian reflector’s primary mirror could lead to better performance and easier collimation.

Many telescopes have mirror mounts that are less than ideal. Some hold the mirror in place with clips that project over its surface and introduce image-harming diffraction effects. Others have adjustments that require tools or are so frustrating that observers rarely attempt to properly collimate the optics. Some cells effectively seal the mirror from the outside air. With no provision for ventilation, it is virtually impossible for the primary to cool down to the ambient air temperature — crucial for sharp images. Some mirror cells have all these problems!

Build this simple device for steady binocular views of the night sky.

I love binocular astronomy. At least, that’s my excuse for cluttering the house with a dozen (at last count) of these double-barreled optical wonders. Recently, my collection expanded to include particularly heavy 10×50s and inexpensive 15×70s. For the first time I really felt that I needed some kind of binocular support.

Too big, too small, or just right? Making sure your reflector’s secondary mirror is the correct size is a straightforward task.

The Newtonian reflector has many strengths, not the least of which is that it consists of just two elements: a precisely shaped paraboloidal primary mirror and a flat diagonal secondary mirror. Yet for all its intrinsic simplicity, confusion abounds when it comes to the optimum size of the diagonal. Many amateurs, and apparently even some telescope manufacturers, seem unsure as to how to choose the correct size for the diagonal. So how big should it be? That depends on several design parameters and some personal preferences.