Reflector or Refractor: Pros and Cons

Reflector or Refractor:  Pros and Cons

If you're just starting out with astronomy you have some decisions to make.  There are 2 types of telescopes and both have benefits and limitations.

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Amateur astronomers have a simple decision to make when they are just starting out.   What kind of telescope should I buy?  Most people will tell you there is a simple choice between a scope called a refractor, or a scope called a reflector.  They have unique characteristics, strengths and limitations. 

 

However, there are two unique challenges you need to understand related to the refractor/reflector decision:  Chromatic distortion and Collimation.  There are also some strengths and limitations related to viewing angle, but let's get through the two "C's" first.


Chromatic Distortion

Chromatic distortion affects refractors.  It's the classic telescope design used by Galileo and allow lenses in a certain alignment to magnify objects.  The occasional problem at high magnification is the way that light behaves.  Light passes through lenses in a refractor and is bent and modified to form an image.  Given the fact that light disperserses through any lens, you may not see the true color of an object.  Chromatic distortion is a failure of a lens to focus all colors to the same convergence point. 

Chromatic abberation lens diagram.svg.png

 

Can you fix it?  Not really although a longer focal length (the length of the tube on your scope) can compensate.  NASA has done significant research on the distortion, but even they admit it's difficult to manage.  The bottom-line is simple, if you choose a refractor you will simply have to accept that you will have some degree of chromatic distortion at some point. 

 

On a positive note, refractors are excellent for observation of near-earth objects such as the moon and the planets.  If you enjoy spending your time studying our solar-system, a refractor is the right choice for you. 


Collimation

Reflectors don't have this chromatic issue given that the construction of a reflector is essentially designed around mirrors that magnify and reflect light.  However, reflectors present a unique alignment challenge called "Collimation."  The fundamental challenge with any reflector is to make sure the light captured at the base of the tube in the polished mirror is accurately directed towards a small mirror at the top of the scope directing the image to the eye-piece.  It sounds easy enough and is fairly basic, but if the base mirror or reflecting mirror to the eye-piece is out of alignment you need to "Collimate" your scope. 

C8 collimation

 An example of good collimation: Image by Jeremy Stanley

A simple way to do this is with a "collimator."  It's fairly inexpensive and uses a laser beam to help you align your adjustments.  Most collimators come with full instructions including the usual warnings about looking directly into a laser beam.  If you purchase a reflector you might want to purchase a collimator as well. 

Owl Optics collimation

A reflector scope being collimated

Reflectors are good for near-earth objects, but are also the scope of choice for observing distant galaxies or moons of Jupiter or Saturn.  They're also more economical relative to a refractor for the viewing power.

 

The general consensus is that refractors are typically used for viewing of the moon and planets, while the light gathering ability of a reflector are best for viewing of galaxies and deep space objects.  However, a reflector also works quite well for viewing the moon and the planets so the decision is up to you.


Viewing Position

One other consideration is related to viewing position.  A refractor and a reflector are wonderful when we're watching Venus rise on the horizon in the western sky or the full moon above the horizon in the east.  It all becomes a bit problematic when we're viewing objects directly above.

 

A refractor with a short focal-length (a short tube) is not a problem especially if you use a 90° elbow.  However, you may need a high tripod and most of us sit in a chair when using a refractor in any position.

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An example image of a high tripod used for this large refractor due to the viewing position at the back of the telescope. 

 

A Reflector is typically a standing proposition unless you're viewing objects on the horizon.  This is both comfortable and easy for adults, but can be a problem for children.  That's something to think about with regards to scope choice.  Refractors tend to favor a lower viewing position, while reflectors tend to favor a taller viewing position. 

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Reflector telescope showing the eyepiece at the top.

 

Beginner Aperture Sizes

Traditional sizes for refractors and reflectors range from 2.4 inch (60mm) and 3.1 inch (80mm) for refractors, and 4.5 (114mm) inch and 6 inch for reflectors.  These are the most popular sizes for most amateurs.

 

Any new scope should have at least 1 eyepiece, and often 2 or 3.  Eyepieces are rated by millimeters (mm), with smaller numbers indicating higher magnification. A 25mm eyepiece is common and appropriate for most beginners.  You may have others that you can drop into your scope to increase magnification, but make sure you are centered on your object and understand its movement.  The larger the magnification, the greater the movement of any celestial object.  This is another reason why collimation is so important with reflectors. Here is an article on choosing the right eyepieces for your telescope.  


Alternative Type of Telescope

A third scope alternative is the Schmidt-Cassegrain design.  This essentially combines the efficiency of a reflector with the clarity of a refractor.  Celestron is the most popular brand name for this combination.  They are very portable but tend to be expensive. 


They are easy to use and often have simple and direct connections to keypads, computers and software.  You may have some collimation to do with this scope as well if it gets out of alignment. They are also easy to use for children. 

 

Over time, you may find yourself with more than one scope of different designs.  The first decision you have to make is finding the right scope for you, your friends and your family. 

If you are looking for a telescope, have a look at the find a telescope guide.

Find more on: Astronomy Equipment

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