Buying Your First Telescope

So, you want to buy your first telescope, and you’re wondering what you should get…

Actually, there already are a variety of excellent resources that passionate and knowledgable amateurs have put together. Michael Edelman’s Heretic’s Guide to Choosing and Buying Your First Telescope is comprehensive, reasonable, and I was pleased to see he basically had the same recommendations I do. Ed Ting, who’s a legend in the amateur astronomy community for his comprehensive telescope reviews, also has very good Advice for Beginners.

For readers who can’t bear to leave Bicycle Astronomy for even a second, (I understand!) I will barrel ahead with this post, and outline my own recommendations, even if it overlaps quite a bit with Michael and Ed’s pages, and in far less detail. (It turns out this post just grew and grew. Well, here it is…)

starparty2 guide

Understanding telescopes, mounts and eyepieces

In astronomical usage, the most important thing a telescope does is collect and focus light; more light than the human eye can collect, the more the better. With a telescope, we can see things that are too faint with our unaugmented eyes. Telescopes also magnify an image, but when purchasing a telescope magnification is not the main factor…aperture is. Aperture is the diameter of the light collecting optic, or objective, so astronomers talk about a 4″ scope or a 6″ scope or a 200″ scope, like the Hale Telescope at Palomar, whose primary mirror was cast in nearby Corning. For beginners, I would recommend a telescope in the 4-6″ range.

Jean-Luc_Picard,_Encounter_at_Farpoint

Listen to Jean Luc! Department store scopes are often useless, and appear to be part of a decades-old plot to destroy (especially young) people’s interest in astronomy.

Anyway, commercially produced telescopes (the kinds that you do want to consider buying) are usually one of three basic optical designs. Refractors have lenses at the front that collect and focus light to an eyepiece in the back of the tube. Pirates used these, but not before Galileo basically birthed modern science with one. Reflectors use mirrors instead of lenses, and the primary mirror is at the bottom of the telescope tube, with (most commonly) a smaller secondary mirror suspended at the front of the tube, which bounces the image to the side where the focuser and eyepiece is (got that?) Isaac Newton invented the particular reflector configuration I just described. We call it….a Newtonian or “newt” for short. Lastly there are catadioptric telescopes like Schmidt-Cassegrains (“SCTs”), which have a lens and a secondary mirror on the front, and the primary mirror at the back. The Cassegrain part of the name comes from the focus point, which is behind the primary mirror in the back of the scope.

Here’s a handy-dandy sketch I made of the three primary telescope types (click on it to see a bigger version, which will open in a new window).

telescopesketch

The telescope optical tube collects and focuses light, but it needs to be pointed, and held, and this is the job of the mount. The simplest kind of mount is called an alt-az, which is short for altitude-azimuth. These mounts are usually very simple, inexpensive, and easy to use. They move up and down (altitude) or left and right (azimuth). Dobsonian is a species in the alt-az genus that sort of resembled a cannon mount. They are usually close to the ground, and the altitude action is produced by large circular or semi-circular bearings.

One of the challenges of using a telescope is that the things we want to look at are in motion. Or rather, the earth is in motion. We are spinning, which makes celestial objects (including our sun) to seem to rise and set. With an alt-az mount, you have to nudge the scope to keep an object in the eyepiece, to compensate for the spin the earth inherited from the disk of gunk that it congealed from around our sun, long ago. Equatorial mounts have motors that can compensate for the earth spinning. They are usually heavier compared to the aperture of scope they can carry, and are more complex to set up and use. I would not recommend an equatorial mount for a beginning astronomer.

Eyepieces complete the optical system of a telescope. Their job is to magnify and focus the light collected by the telescope’s objective. Telescope apertures are often quoted in inches, while eyepieces are almost always labelled in millimeters. I have no idea why. The longer the focal length of an eyepiece, the less the magnification and the wider your field of view will be. 32mm is a popular low-power, wide angle focal length. 7mm, on the other hand, produces more magnification. Generally you’ll need two or three eyepieces; a wide angle/low power, a medium power, and a high power for planets and other smaller objects. Eyepieces are a world unto themselves. Ed Ting’s page linked above has some good advice, so I won’t repeat it. I will list my current eyepiece line up: a 24mm Explore Scientific wide angle with a 68′ apparent field of view, a few old Clave plossls (25mm, 20mm, 12mm), a Brandon 8mm (made nearby!) and a Takahashi Hi-Or 4.8mm for high power viewing. Most people won’t need this many, but many observers have far more eyepieces than that.

On Star Maps and Droid Scopes

The major telescope companies now sell (at scary low prices) fully automated telescopes that, once you turn them on, align themselves (usually relying on GPS signals) and will find any object you ask it to. Or push another button and it will lead you on a guided tour of the night sky. I call these “Droid Scopes”. They are remarkable. And, in my opinion, terrible for a beginner. An astronomer, even an amateur, should learn their way around the night sky, first with their naked eyes, then with the telescope. This not only provides the person with a sense of orientation and a comforting ability to decode the night sky above them, it also places those telescopic views into context, so that, for example, you know both where the Orion Nebula is in the sky and what it looks like through a telescope. A droid scope robs the astronomer of the former, and decontextualizes the latter; part of the thrill of observational astronomy, like bird watching, is in the “hunt”. There’s an additional reason I don’t support the robot telescope idea for beginners, but that will have to wait for the “expectations” section below. I need to stay on target, R2…

Your first step should be to get to know the night sky. The nice thing about this phase in the development of an amateur astronomer is that it is, for the most part, free. Go to www.skymaps.com and print out a free Evening Sky Chart for your month. I posted about free sky charts a while ago (it’s oddly my most popular post by far) and I had this to say about the Evening Sky Chart:

In my opinion, this map is far better than the color ones published by Sky & Telescope and Astronomy. They’re more readable, have better information for a beginner, and, THEY’RE FREE! The prominent feature of the two-page (one front and back) publication is a large circular map of the sky with instructions for use. To the left of that is a calendar of astronomical events that month. The B side has notes, instructions, a very helpful glossary, and a list of celestial objects that you can see with the naked eye, in binoculars, and with the aid of a telescope. For all the information that is packed in, the design is extremely clean. It’s a work of graphic design art. It’s perfect for learning the constellations, and finding planets and the brightest deep sky objects.

As you or your child master the constellations and the brightest telescopic objects, you will soon need a more detailed sky atlas. You have a few options at this point. The first is one of the other free downloadable sky charts in my post. You can also buy a commercial star atlas. Sky Publishing’s Pocket Sky Atlas is an economical, beautiful choice. The third option is a planetarium program like Sky Safari, on your smart phone. I recommend this if you have a smart phone or iPad. There’s a fairly up to date list of astronomy apps here.

The moon is one of the first things you are likely to look at with your telescope. It’s easy to find, and, frankly, stunning. amateur astronomers who hunt distant, faint galaxies usually curse the moon, because when it is full it washes out their prey, even from large aperture telescopes. But as an object of study, the moon is a pure gift. Observe it when it’s less than full, and concentrate on the terminator between day and night…you will see mountains, craters, ridges, it’s amazing. There’s a great moon atlas app for iOS called…Moon Globe. It’s free, too.

MoonGlobeEddington4a

A screen shot of Moon Globe, with a box showing information on one of the craters.

Your finder scope

The best finder scope for beginners, heck, for just about any astronomer, is one in a category called “unit power finders”. All of hte ones available today trace their heritage back to the grandaddy of them all, the Telrad. Company7 has a great page about the Telrad’s history. Basically, a Telrad is like a simple head’s up display you might recall Maverick using to “lock on” to those enemy Migs in Top Gun. It’s a slanted clear window that reflects back an image projected from below. The Telrad has a three concentric circle target, 4′, 2′ and 1/2′ for the center circle. You look at your star chart (some of which come with acetate overlays with telrad targets on them) or your planetarium app (which often have a Telrad target you can enable as your select box), then you align your actual Telrad’s red targets onto the actual stars in the sky. It’s amazingly easy. The Rigel Qwikfinder is another unit-power finder that’s a lot lighter than the clunky Telrad, and is also not quite as nice optically, but for smaller scopes I prefer it. Many beginners’ scopes from enlightened companies now come with similar “red-dot” finders, which project only a single red dot, but work fine. Make sure you’re either buying a scope with one of these finders, or that you get one at the same time.

Locked On

Locked on. Adam Collins (M104 on Flickr) showing the observer’s view through a Telrad finder mounted on a telescope. (Creative Commons)

The use of a Telrad enables an observer to use another nifty navigation aid, this one definitely in the lo-fi category: Astrocards. These index cards each cover several deep sky objects, each of which is plotted on a simple single-constellation chart that you can hold up to the sky in front of you. These also have Telrad circles, so you just orient your own Telrad so it’s in the same position vis-a-vis the surrounding stars, and you should see your target in a low-power field of view. Recommended, though you can’t check Facebook on them.

Expectations

We live in a 3D, CGI-infused world. Sadly, people are so saturating their brains with stimulating imagery that the poor real world is losing its shimmer. It’s a problem. Part of what I try to do with astronomy is reestablish the actual, physical universe as the source of beauty and inspiration. I once had a student in my astronomy observing session at a local college look at his iPhone, which had an image or and data about M13, the Great Hercules Cluster, on screen. I was about to show him M13 through my telescope. “This,” he said, lifting up his iPhone and pointing at my telescope, “makes that obsolete.” A little part of my soul died. The iPhone simulates. The telescope collects actual primary sources, photons that have travelled for thousands of years to perchance activate a rod or cone at the back of our eyes.

Telescopes and cameras are so good these days, we are starting to photograph galaxies that are so far away, they date from the first billion years of the universe. Google “Hubble Deep Field” and you can see hundreds of distant galaxies in one stunning, universe-rocking photograph. Even amateur astrophotographers are offering vistas of incomparable beauty. These are not inaccurate representations (far from it) but they are not representative of how we can see these objects from space. The reasons why are complex and I won’t get into it here, but suffice to say astrophotographic equipment can do things the human eye/brain combo cannot, like integrate hundreds of images into a brighter, more detailed composite, or compile an image over many weeks, like the Hubble Deep Field.

This is that other reason I don’t like droid scopes that do all the work for an observer. It diminishes the view because really, you did nothing to get yourself there. Water does go down better if you’re been walking in a desert for a while. I have tried it.

Anyway, it’s also important to calibrate your expectations for your telescope. So here’s an astrophotograph of M42, the Orion Nebula:

The Great Orion Nebula (M42)

Thomas Shahan, the astrophotographer who made this image, combined 56 frames, each of which took 30-50 seconds of light gathering time. The result is an excellent, detailed image, impossible for backyard astronomers to achieve just a few decades ago.  It’s also not what M42 will look like through even the largest telescopes. To capture telescopic views in a realistic way, we have to turn to sketches. Here’s one by an amateur astronomer in Israel, Michael Vlasov.

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If you click on the photo, it will bring you to Michael’s website, where you can see the original sketch he did at the eyepiece…he doesn’t produce these masterpieces entirely while shivering next to a telescope! Check out his sketch gallery for more realistic views of what you might see through a telescope eyepiece. This is a better way to calibrate your expectations (though Michael observes from very dark skies, so many of the more diffuse objects will not appear as bright to most of us in suburbs, let alone cities.)

Jean-Luc_Picard,_Encounter_at_Farpoint 2nd

If you’re buying your first telescope, you shouldn’t be yet thinking about astrophotography. Astrophotography is thrilling (well, for some people), rewarding, expensive, time-consuming, and requires a lot of equipment. And expensive. Did I mention expensive?And it can be incredibly frustrating. If you do want to try astrophotography, start with a DSLR camera, a wide-angle lens, tripod, and try some star trails. The Google can help you out, as always.

Finally, a Recommendation!

So after all that, what should you buy for your first telescope? It really depends. The two sites I linked to above have lots of good advice. It depends on who’s going to be using it, for what, and where. Old people may want a lightweight scope they can carry in and out easily, and one that places the eyepiece in a comfortable position for a tired back. Young people may appreciate a scope that puts the eyepiece at their eye-level, and that they too can carry around. If you live in a city, you might want a larger aperture scope to see a bit more through the light pollution. If you’re in the country, you can get away with a smaller scope and see more, but you might also want a much larger scope as you’ve got the skies for hunting down very faint galaxies and nebulae. And of course there is budget.

Telescopes are not one size fits all. Generally though, for all but small children who may not stick with it, I think a 6″ f/8 newtonian reflector on a dobsonian mount is about the closest thing to a general purpose beginner’s scope as anyone has ever come. I spent several years with a 6″ f/8 as my only telescope, and I still think it’s a sweet spot for portability, comfort, and light-gathering ability. It will show you a lot of deep sky objects (especially if you live in or take to it to some dark skies), will provide excellent lunar and planetary images, and well, it’ll do most things well. I still have mine, matter of fact, and here it is:

6f8-1

Since not everyone can buy my telescope, I’d recommend Orion Telescopes’ XT6. Though I’ve never owned this Orion, I have used one, and they are well made, sturdy, optically fine telescopes that are a bargain. The 6″ f/8 used to be out of reach of most beginners, but mass (Asian) production has dramatically changed the telescope scene today. The Xt6  is about 48″ tall when looking at the zenith and weighs about 30 pounds. Right now, Orion has a sale: for $300, you get the scope and mount, a red-dot finder, an eyepiece, a barlow lens which will double the magnification of that eyepiece (I’d still get a high-power eyepiece, perhaps a 6mm or so), a planisphere, moon map, and some other goodies. Wow.

If you’ve got small children who you are fairly sure will be into it, then the Orion Starblast 4.5 might be more their size. If you’ve got small children who you’re not sure will be into it or not, you can spend even less ($50) on a Funscope. But honestly, your best bet with young children in this category might be to make astronomy your hobby, and see if they take to it, in which case I’d still look at the XT6. They might need a step-stool to see through it when you’re looking near high in the sky, but it will yield brighter, more detailed views than the smaller scopes I mention here. The XT6 scope has a little brother, the XT4.5, which is smaller and more kid friendly, but still a very good scope for adults. It’s just that at the moment the XT6 is the same price, so it’s hard to recommend it unless you really value the smaller size. And if you live in a city or light polluted suburb, the extra aperture of the XT6 would be welcome!

I’m sure this discussion raised more questions than it might have answered. Feel free to ask a question in the comments, I’ll do my best.

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