How to Buy a Telescope for Yourself

Throughout this blog I have made reference to viewing various celestial objects and events through binoculars or a telescope, and this works fairly well if you already own one or both such instruments. However, suppose you don't own either one - or, suppose you own a pair of binoculars but are itching to buy a telescope. It is perhaps the most common question that novice astronomers and non-astronomers ask experienced amateur and professional astronomers: "I'd like to purchase my first telescope. What telescope should I buy?" Today I will provide you with some instructions and advice that should (hopefully) be of use to you as you begin shopping around. In a future entry I will explain how to purchase a telescope for your child.

Before You Begin
If you are new to the night sky, then I would suggest buying a pair of nice binoculars first. You can drop $100 at Walmart for a cheap telescope that will quickly disappoint, or you can buy a quality pair of binoculars at the same cost that will provide better image quality. Yes, you are losing out on magnification (although don't buy the pitch from the cheap retail telescopes that claim 500X magnification!), but what you are gaining is an easily-transported, well-made optical instrument that will introduce you to the night sky before you get lost using a new telescope.

Here is a common scenario: you enthusiastically run to the store to buy a telescope, spend $150 on one that promises incredible magnification and comes in a box plastered with amazing images of planets, nebulae, and galaxies, then take it home and don't know what to look at. This occurs because the telescope didn't come with a drive motor or computerized paddle - you know you'd like to look at Saturn, but don't even know where Saturn is.  You go inside also wishing you knew what season the constellation Orion was visible, pack the telescope in its box, and it subsequently collects dust.

Is the best choice to go buy a nice computerized telescope?  Not unless you'd like to spend $500 or more on something that will likely sit in your garage or basement for the foreseeable future.  Buying a nice pair of binoculars and a star atlas allows you to fall in love with the night sky.  Go outside, lay on a blanket, and use your star atlas to guide you from star to star through a constellation.  Binoculars have sufficient magnification (the first number in the specs: for example, "7x50" binoculars have a magnifying power of 7X and an aperture of 50 mm) as to reveal rich open star clusters, the phases of Venus, the Galilean moons of Jupiter, and exquisite lunar features.  Star-hopping like this helps to familiarize yourself with the night sky.  Using star maps from an atlas or an astronomy magazine, you can become an expert in night-sky viewing.  Then go buy a telescope.

Types of Telescopes
There are several different kinds of telescopes that can be differentiated by the optical elements they utilize and the mounts on which they are built.

1. Refractors:  Refracting telescopes are long and narrow tubes with a glass lens on one end and an eyepiece on the other:
   
   These telescopes can be on equatorial mounts (shown above) or altitude-azimuth mounts (which are easier for pointing, harder for tracking).  Cheap models will have one simple lens at the aperture (the big end), while higher quality models will have a two-piece (achromatic) or three-piece (apochromatic) compound lens.  The more lenses, the better the image quality because these additional lenses are correcting for an effect called "chromatic aberration" where different colors are focused at different distances by the glass lens.  Of course, the more compound the lens, the higher the cost as well.  Many refractors are not motorized, although some of the high-end ones can be.
2. Reflectors:  Reflecting telescopes utilize mirrors to focus the light rather than an aperture lens:
   
   These can be long or short, and most often have an open aperture with a mirror on the lower end.  The light is reflected off this mirror to a smaller, flat mirror up near the opening and then directed out the side of the telescope through the eyepiece.  Reflectors do not have chromatic aberration and typically offer more bang for your buck as far as aperture size goes.  The larger the aperture, the more light is collected - producing a brighter image with better resolution.  Equatorial mount reflectors can come in both motorized and non-motorized forms.
3. Dobsonians:  Dobsonian telescopes are simply reflecting telescopes that sit on the ground in an altitude-azimuth mount:
   
   Other than this mount difference, they have the same characteristics as other reflectors while also providing much longer focal lengths - giving you higher magnification capabilities (provided you have the right eyepieces).  Dobsonians are almost never motorized, but many do come with a computer paddle that tells you which direction to move the telescope by hand.  This is a reasonable compromise between paying less for a non-motorized telescope while also having the advantage of a built-in object library.
4. Schmidt-Cassegrains: The final "general" category is the Schmidt-Cassegrain Telescope (SCT) that uses both a lens and mirrors to focus light:
   
   These provide great image quality, high magnification potential, and are usually computerized...but they are also expensive. 

Choosing a Telescope
When you are ready to purchase your first telescope, there are a number of factors that you should consider.  These factors are (in no particular order):

1. Budget
2. Optical quality / aperture size
3. Portability
4. Time available for use
5. Ease of use

Budget:  Most people consider budget the primary factor, and this is reasonable.  When buying a telescope, you can find them ranging in price from $100 to $10,000!  My first tip: don't run to a department store and buy that $100 one I mentioned earlier.  While affordable, these telescopes are mass-produced with low-quality optical elements and a wobbly mount.  Why does the mount matter?  If your telescope is constantly shaking and vibrating when you touch it and doesn't stay aimed at anything without drifting, your experience will be extremely disappointing.  Having a stable, sturdy mount is almost as important as having quality optics.  For your first telescope, plan on spending around $300-$400.  This will ensure that you have struck a good balance in quality and size for your first telescope.  Which brings me to the second factor...

Optical quality:  If the quality of the lens or mirrors in your telescope is poor, your viewing experience will be poor as well.  Department store telescopes are made with cheap glass lenses that offer more aberration than acclamation. A telescope retailer (either a store or online) will provide better quality options.  You want a telescope that uses quality lenses or mirrors!  This ties in with aperture size too.  In general, bigger is better.  However, bigger is also more expensive.  You'll need to strike a balance.  You can use a diagram like this to determine your optimal aperture size:

"Limiting stellar magnitude" in this diagram simply refers to the faintest object you can see through the telescope.  Larger numbers correspond to fainter objects.  Between 6-10 inches in aperture diameter typically provides a reasonable performance for its cost.  Refractors have smaller apertures than most reflectors, but can provide better images if you pay for it.  For reference, planets are bright, galaxies are faint.  Planets are easily visible in nearly all telescopes, while galaxies are only visible with larger apertures - typically greater than 10 inches.

Portability:  Will you be taking your telescope on trips, or will it always be used outside?  Will you be the one using it, or will your child?  Portability is an important thing to consider depending on your plans for the telescope.  Larger telescopes and sturdier mounts are heavier to move around and sometimes require a bit of dis-assembly to transport.  Additionally, if your telescope has a drive motor and/or computer it may require a source of electricity.

Time available for use:  How often do you envision the telescope being used?  Once a week?  Once a month?  Only once?  If you will use it a lot, you may wish to spend more on one that will provide a lifetime of viewing options - this generally means purchasing a larger telescope with a broad range of eyepieces.  If it will be used only on occasion, then don't spend more than $500.  If this might be used once or twice before interest in it wanes, don't spend more than $300.

Ease of use:  How good are you at learning to use new equipment?  Is this for a child or an adult?  Simple telescopes may look "too basic" but they are much easier to use than computerized telescopes.  They act as "point-and-shoot" telescopes, and all you really need to learn is how to point them using the axis knobs.  However, you also need to be familiar with the night sky.  Motorized, computerized telescopes make it very easy to find things...provided that you have it plugged in and set up properly and have done a correct alignment using several stars in the sky.  Motorized telescopes have thicker user manuals.

The Final Choice
After you have considered all these factors, it comes down to making a choice.  Many amateur astronomers will go with a 6- or 8-inch Dobsonian reflector and be very happy with it.  Others prefer to buy a nice 3- or 4-inch refractor and get superb views of solar system objects.  Motorized SCTs are extremely hard to find under $700 unless you buy one secondhand.  All things considered, I prefer to recommend getting as much aperture as you can afford.  A great 4-inch refractor is nice, but at the cost of something like that you can get a 12-inch reflecting telescope with a drive motor that will allow you to see many more types of objects than the smaller refractor.  Consider the factors I have mentioned above carefully, then talk to a telescope retailer to find one that will best fit your desires.

Resources
Check out some of these manufacturer websites to see your options and their costs:

• Meade
• Orion
• Celestron
• Galileo