Buying A Telescope

ITS OK TO BUY ANY TELESCOPE YOU CAN AFFORD AS LONG AS YOU RECOGNIZE YOUR EQUIPMENT'S LIMITATIONS AND YOU REALIZE THAT THERE MAY BE OTHER BETTER OPTIONS.

ANY TELESCOPE THAT HAS TAUGHT YOU SOMETHING WAS MONEY WELL SPENT.

THE BEST TELESCOPE WILL ALWAYS BE THE ONE YOU USE THE MOST!

A LITTLE BACKGROUND INFORMATION

INTRODUCTION

     Choosing the right telescope can be just as important as learning the constellations. There are so many choices and price ranges on the market today that it can seem a complicated landscape of equipment to navigate. With such a variety of equipment built to specialize in different areas of astronomy it is safe to say that there is no such thing as an ultimate one telescope that does all. But you don’t have to break the bank to get a decent scope that will last you a lifetime. At the same time you don’t want to spend hard earned cash on something made cheaply that wont last but a few years before it heads to the junk yard. All to often this last scenario happens to the uninformed novice and it completely turns them off to the hobby of astronomy… permanently. I’m often reminded of the advice a very good friend of mine once gave. “The best telescope is the one you use the most.”

700X MAGNIFICATION!

     Many times a person’s first encounter with a real telescope is in a department store. Usually around holidays like Christmas, retail stores pack their shelves with telescopes offering huge magnifications at a relatively cheap price. Getting hooked on this sort of advertizing is one of the first mistakes beginners often make. There is a term in astronomy called useful magnification. In other words magnification is only useful at magnifying details up to a certain point. After that any more magnification only serves to magnify a fuzzy blob making it a larger fuzzy blob. The average small backyard telescope typically has a maximum useful magnification of anywhere between 200X-350X, give or take. Anything more than that is generally made useless by a combination of factors such as the size of the scope and seeing conditions.

     The resolution of or the amount of detail you see in an object through a telescope is ultimately governed by the size of the telescopes primary optic (its largest mirror or lens). To gain resolution you would have to increase the size of your telescopes primary. This is why professional astronomers build ever larger telescopes. Thus it’s not the magnification of a given eyepiece that is important but rather the size of the diameter of the telescope’s primary optic.

REFLECTOR VS REFRACTOR

     There are various reasons for choosing a reflector over a refractor or vice versa but its not a huge issue when starting out. If you graduate to the intermediate or advanced levels of amateur astronomy, like the rest of us amateurs you will probably end up having a collection of scopes too. Typically its important that the aperture of any reflector be a minimum of 4.5 inches in diameter. Anything smaller and you might as well get a refractor or binoculars. As for refractors a bare minimum diameter is 60mm. The recommended size for a small refractor is between 80mm and 90mm. Anything less than 60mm will be disappointing. Keep in mind that the bare minimum for binoculars is a 10X50, where 60 represents the diameter of the binoculars primary lens(50mm). A 60mm refractor is essentially a “monocular”.

     When it comes to prices, the reflector always wins over a refractor. Its cheaper to make a larger reflector than it is a refractor of the same size. With reflectors you get a bigger bang for your buck. The larger reflector gives you an advantage when it comes to faint light sources from deep space objects. Remember that size does matter when it comes to teasing out details and collecting photons of light from galaxies far, far away. Reflectors are also not subject to chromatic aberration like refractors. The lens of a refractor has difficulty focusing the violet region of the visible light spectrum at the same focal point as the rest of the spectrum. This produces a purplish coma around bright objects. There are filters for refractors, called fringe filters, that can block the violet part of the spectrum and thus block the purplish coma. However, refractors do have something to offer over reflectors. When it comes to viewing bright planets and the moon they are awesome. For some reason the details on planets and lunar features seem sharper as seen through refractors. Refractors are also well suited to astrophotography.

EQUATORIAL MOUNTS VS ALT-AZIMUTH

     The telescope mount can be one of the big hang-ups when it comes to learning how to use a telescope, especially with equatorial mounts.

     The easiest mount to use is the simple alt-azimuth, where the alt or altitude axle moves the telescope up or down, and the azimuth axle moves the telescope left or right. No complex alignment to the celestial pole is required but you must move the telescope in both altitude and azimuth to track an object across the sky. Dobsonian telescopes and some higher end “goto” scopes use this type of mount.

     There are advantages to having an equatorial mount over the simpler alt-azimuth. The most obvious being that you are able properly orient your telescope relative to the earth’s spin axis and your latitude location on the globe. This allows you to track an object with one axis alone. However, the equatorial mount must always be aligned to the celestial pole and unless your telescope is in a permanent location you will have to do this once before every time you observe. The issue with low end budget scopes and equatorial mounts is that they usually don’t come with a motor to automatically track for you. Some of them still have a gear in place so you can purchase the motor separately. Equatorial mounts are generally better for higher end “goto” scopes with heftier mounts used for astrophotography or long periods of intense visual study of an object. This doesn't mean you shouldn’t get one on a budget scope. If you learn how to use an equatorial mount in the beginning, you’ll be ready to handle it when it comes to purchasing a higher end model for advanced purposes.

EYEPIECE BARREL SIZE

     There are two standard eyepiece barrel sizes on the market today. These are 1.25” and 2”. Older and sometimes newer cheap scopes came with a smaller .965” barrel size which is all but nonexistent nowadays. Make sure that the scope you choose accepts either the 1.25” or 2” sized eyepiece barrel or both.

WEIGHT

     Consider the weight of the telescope you buy. Remember that you will have to carry it outside every time you want to observe. Larger scopes are heavier and more cumbersome to transport. I can guarantee from personal experience, that there will come a time when the thought of carrying all that weight outside will be the deciding factor on when and if you observe on a given night at all. If you are worried that a telescope is a little on the heavy side, try looking for its weight in the dealer’s specifications section. Duplicate the scope’s weight by filling a large bag or suitcase with an equal amount of weight.

BRAND NAMES

     I recommend seeking out and paying a little more for a well known brand. This ensures that you wont have to deal with an odd ball scope that virtually no one has ever heard of and who’s manufacturer provides no support in the form of upgrades, accessories, or help with problems. Meade, Orion, Celestron, and Zumell are just a few of the brand names that amateur astronomers purchase products from.

THREE CLASSES OF TELESCOPES

THE BUDGET CLASS

      The budget telescope is typically defined as any telescope priced under $200 in today’s market. They are typically either a reflector or refractor and can come on either an alt-azimuth or equatorial mount.

     While it may be ok to start out with a budget telescope you must do so with the understanding that you will eventually want to upgrade to something better. Understanding the limitations of a budget telescope and pushing it to its limits can still be a worthwhile learning experience.

     Budget telescopes are budget telescopes because the manufacturers have made some sacrifices in the quality of design and or materials to get you that bottom line price. Most department store models fall into this budget class. Sacrifices in design and materials usually mean that plastic parts end up breaking and, over time, spindly mounts tend to become loose and shaky. The quality of included eyepieces may also suffer and some budget scopes still use the old standard of .965” eyepiece barrel size.

THE TABLETOP TELESCOPE

     A subdivision of the budget class is the “tabletop” telescope. While the quality of the instrument may be top notch, including the eyepiece, the scope lacks one all important thing. A sturdy mount. Its not that the little dob-like tabletop mount the scope came with is unstable, it’s the fact that the mount is so short you have to find a table to sit it on. I have yet to meet a table, unless its made of concrete, that is sturdy enough to sit a telescope on for a proper observing session. So, unless you intend to construct a sturdy mount that you can haul around with you or you use the scope in an area with concrete picnic tables, I wouldn’t even consider purchasing a tabletop telescope. Its just not worth it.

THE DOBSONIAN CLASS

     By far, in my opinion, the best choice on the market for beginners to date, and my personal favorite for visual astronomy, are the dobsonian class of telescope. These simple alt-azimuth mounted Newtonians are ultra easy when it comes to budget vs size, transportation, and setup time. I like to call them “point and shoot” telescopes because once they are assembled and the finder scope aligned, all that’s left to do is to pick it up, take it out the door, set it down at your site, and start observing. There is no frustrating half hour or more spent each night trying to align your equatorial to the sky.

     Some dobsonians now come with a handheld computer that helps you point the telescope at objects in the sky. The main issue with these is that you still have to undergo an alignment procedure to align the computer to the sky with each observing session. Sometimes you spend more time on the alignment procedure than its worth. It generally pushes the price of a dobsonian up by about $100 USD or more. You can save yourself some time and money by learning to read a star chart and remembering where an object is located in the sky.

     The dobsonian may be a little more expensive than the budget telescope but you do get a lot more in the form of quality and service to your hobby. Expect to spend anywhere between $200 and $800 USD for a small to medium sized dobsonian, though they can run much higher in size and price.

THE GOTO CLASS

     Higher end scopes usually have electronic controls and computers integrated into their mount. This gives them the luxury of being a “goto” scope. Press a button and the scope will “go to” a selected object. Most are either large refractors or catadioptric types like the Schmidt-Cassegrain or Maksutov-Cassegrain. Some are Newtonian but large Newtonians on hefty mounts are less common because of the necessity of a ladder to reach the eyepiece, not to mention transport issues. Among the “goto” class there are even a few motorized dobsonians beginning to appear on the market.

     The computer on any “goto” mount usually has a database of thousands of objects and can even take you on a tour of objects you never knew existed. The automatic, hands free tracking feature allows you the opportunity to spend more time studying an object intensely, teasing out details that you never knew where there before. A higher end “goto” mount is usually also more robust in that it provides a sturdy base for you to image the objects you see through your telescope.

     A “goto” scope can be equatorially mounted or alt-azimuth mounted. Either way there is some setup time involved before you observe. Equatorially mounted “goto” scopes require you to first physically align the mount to the celestial pole and secondly perform a procedure to align the computer to the sky as well. To the novice this can be a little daunting and you may give up on it the first couple of times. Persistence pays off. Even if you are never quite able to get the computer aligned just right you can still use a “goto” equatorial mount with a basic polar alignment to automatically track objects.(I confess I do this with my own Meade LXD-55.)

     Alt-azimuth mounted “goto” scopes also require an alignment procedure, though these days some of them are so sophisticated that you only need to set them up, press a few buttons, and they align themselves using GPS. The only issue with this type of mount is that when it comes to astrophotography you are limited to short exposures. Because the alt-azimuth tracks an object on two axis and does not take into account your latitude on the globe, long exposures will cause the edges of the image to swirl as the telescope tracks an object across the sky. Adapters are sometimes available for alt-azimuth “goto”s that can convert them to equatorial mounts.

     A “goto” scope is not cheap. They typically start at or about $400 USD and can run upwards of $3000 USD or higher.