Are You Thinking About Buying a Telescope?

OneSkyI’ve been so busy with the holiday bazaars and filling orders that I haven’t posted anything directly about astronomy for a while.  But a couple of people have asked me recently about buying a telescope, especially for a child, so I thought I’d offer some general advice.

The first thing that any amateur astronomer will tell you is to never buy a telescope from a department store or any place that doesn’t actually know anything about telescopes.  The low cost scopes they carry are not only usually of poor quality, they are also too expensive for what you get.

But let’s start with some background information.  Telescopes can be divided into 3 categories; refractors, reflectors, and catadioptric (having both refractive and reflective elements).  A refractor is what most people think of when you say “telescope” – it has a lens in the front and an eyepiece in the back.  A reflector (typically called a Newtonian telescope) instead uses a curved mirror.  The mirror is at the back end of telescope tube and the eyepiece goes off to the side of the tube near the front.  There are many kinds of catadioptric telescope, but the most common type is the Schmidt-Cassegrain Telescope, or SCT.

Each of these 3 types has strengths and weaknesses.  Refractors are generally rugged and stable, but easily the most expensive type when you compare the cost per inch of aperture (the diameter of the primary optical element).  Newtonian reflectors, especially in the form of a “Dobsonian” telescope and mount, are probably the most popular type for visual astronomy because they provide the largest aperture for a given amount of money, but require some regular maintenance, especially in larger sizes.  The Dobsonian concept (developed by the late champion of amateur astronomy, John Dobson) reduces the telescope mounting to a simple swivel/tilt mechanism so that emphasis can be placed on getting the largest mirror possible.  SCTs are also popular, especially for viewing small, bright objects such as the planets, because they provide a lot of magnification in a small, light weight package.

Bear in mind that high magnification is NOT the most important attribute of a telescope.  Beyond a certain level, increasing magnification does not provide any improvement in the view for several reasons.  If you have to boil a decision down to a single characteristic, a telescope’s aperture (optical diameter) is probably the best proxy for value.  More aperture means more “light gathering power”, and it is this ability to see dim objects that really defines visual astronomy.  In astro-photography we can simply do a longer exposure to gather more light, but not so in visual work.

An equally important decision is the type of mount you will use.  In particular, telescope manufacturers like to sell “computerized” or “go to” mounts that can more-or-less automatically point the telescope at a selected target.  This is a great idea for the manufacturer because they can charge more for something that is both visually impressive (seeing the telescope move automatically) and seemingly advantageous.  And it can be very useful.  However, it is never as easy to set up and get working as they would have you believe.  Furthermore, using a computer to find objects removes you from actually studying the night sky.  Indeed, many amateur astronomers would argue that finding your own way to a target is a large part of the enjoyment of astronomy.  I’m not one of those people – I use a computerized mount almost exclusively because it saves time and I need that time for long exposures.  However, I do understand and appreciate this aspect of visual astronomy.  It is revealing that I have been doing astro-photography with a computerized mount for 10 years and still can’t find more than a handful of objects without a computer.

I have only 1 specific recommendation for a telescope for a beginner, the “OneSky” telescope from Astronomers Without Borders (click here).  Aside from supporting a great organization, the OneSky telescope is surprisingly good.  It might be too much money and maybe even too big for a very young child, but for anyone else, including an adult beginner, it is capable, compact, and easy to use.

About Greg Marshall

I am a retired electronics engineer and after a few months of enjoying my leisure I began to miss doing product development. My astronomy hobby always needed new solutions to unique problems, so I decided that whenever I came up with a good solution I would try to make it available to others.

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