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Telescope Buying Guide

Buying a telescope is much like buying a car.  Asking a car owner “What car should I buy?” will lead to a multitude of answers.  This can be confusing and even deter you from making the purchase.  My first post discusses my personal experience with the “What telescope shall I buy?” question.  Below is my infographic telescope buying guide to help you with this process.

5 Step Infographic

How to Buy A Telescope by Kevin Francis

Types of Telescopes

What makes a telescope a telescope is that is uses lenses and/or mirrors to magnifiy light from distant objects for your eye to see. There are three standard types of telescopes, reflector, refractor, and catadioptric. The refractor uses lenses. It was first used in the 17th century in the Netherlands. Being first means it is the more common type sold to beginners. Therefore, they are everywhere, in big box stores, hobby shops, toy stores and more.

The reflector uses mirrors and is the invention of Sir Isaac Newton. They are also referred to as Newtonian Telescopes. These are a good first choice for the more serious first time astronomy enthusiast.

Finally the catadioptric telescope, was developed in the 1820s. I think of it as being the best of both worlds telescope, using both glass lenses and mirrors. In addition, they are more expensive then the other types. Buying one of these is a sign of a serioius committment to astronomy or astrophotography.

Telescope Buying with Aperture Envy

When participating at a Star Party, the lines are usually longest at the larger telescopes. The connection is made that the larger the telescope, the further out you can see. This is a common misconception. Yes, it is true, larger telescopes gather more light. However, pushing the limits of visability, without the ability to focus on the object can be a frustrating experience.

What is aperture? This is the diameter of the telescope primary lens or mirror. This is the easiest metric to see as a star party guest. Aperture sets the apparent size of the telescope to the casual observer. It’s most important use, is simply to get at much light as possible to the eye of the user.

By the way, large telescopes are a bear to travel with and are great for home observatories. Choose wisely in this metric.

Focal Length is Key

Focal length is defined as the distance between the center of the primary lens or mirror to the point of focus when focused at infinity. In other words, how far away can it focus from the center of the primary lens or mirror. If you’re most interested in how far you can clearly see, the question to ask a telescope owner is “What is the focal length?” This is what determines how much of the sky is visible in the eye piece. Meaning wide areas of the sky or small, very close views of a single far away object. If you’re the person looking for details at far distances, ignore the aperture envy and focus on focal length. You’ll thank me later.

Focal Ratio: Combination of Aperture and Focal Length

Take focal length divided by aperture and you get Focal Ratio. This is a simple measure of how fast a telescope can gather light. Most telescopes range from f/5 to f/10.

Telscope Buying Guide Final Thoughts

Of course you can spend as much or as little on a telescope. The choice is yours. As for me the choice was based on being able to learn my way around the night sky. The ability to point out an object without using a computer is what drove me to my choice. However, the beauty of this hobby, is that you will do what’s best for you. Good luck and clear skies!