If you’re confused about refractors vs reflectors this article covers the ins and outs of these different telescopes, used by backyard astronomers.
Before I started into astronomy and went looking for a telescope, I thought all telescopes were much the same. I soon discovered I had no idea. There were quite a few variations and refractors and reflectors were confusing.
Main differences between refractors and reflectors
A refracting telescope uses a lens to gather light. A reflecting telescope uses mirrors. Refractors are light and transportable and need little to no maintenance compared to reflectors. The reflector’s advantage is the design can take larger apertures to gather more light.
|Refractor||Uses a lens|
Eyepiece at rear
|$$||Needs less collimation|
Eyepiece at front
Gathers more light
Cleaning of mirrors and tube
Can be subject to dust and humidity
How to Tell a Refractor From a Reflector
You can easily tell them apart. The obvious difference is the focuser and eyepiece in the reflector sits at the front (or the top). And, in the refractor, these parts are at the back of the telescope tube.
Price-wise you can get a small refractor or a reflector telescope for under 200 but pay several hundred more for better quality models in both.
But how easy are refractors vs reflectors telescopes to use?
Refractors require less maintenance.
The trickiest part of up-keeping a reflector is trying to avoid scratches while cleaning the mirror. Fine scratches can be worse than dust for messing with views.
Reflectors need collimating more than refractors. I wrote about this in how to collimate a Dobsonian.
What’s involved with collimation? Collimation is aligning the primary with the secondary mirror and the eyepiece. You can do this manually or with the use of collimation tools. I explain how to collimate an SC telescope in my step by step account.
The bigger the objective in the reflectors, the more regular the need for collimation. In cases of larger reflectors, this could be every time you move it to a new location. But with the right tools and practice, it will only take you 10 mins or so.
What is a Refracting Telescope?
Refractors are dioptric, they use a lens to gather and bend or refract light.
The refractors have a lens at the front. The eyepiece sits at the rear. They have a long, closed tube in which the light must travel in a straight path through to the eyepiece. The larger the lens the longer the tube needed. Hence, why refractors tend to be small.
Disadvantages of refractors: They are known to suffer from chromatic aberrations, meaning colored fringes around the viewed objects. The other issues are spherical aberrations and lens sag.
Lens sag becomes a problem with increased size. It only occurs in larger refractors. Basically, the lens becomes distorted by its own weight.
What to look for: Look for telescopes with compound lenses (different types of glass) to correct color aberrations. Doublets are less costly, but triplets, designed to eliminate this issue, cost more. Parabolic lenses correct spherical abberations.
For astrophotography, apochromatic refractors suit best as they overcome the need for an extra field corrector or space.
What is a reflecting Telescope?
Reflectors are catoptric. They use mirrors to reflect light. One or more curved mirrors are used to make them free from chromatic aberrations.
Cheaper reflectors have spherical mirrors.
Most reflecting telescopes have a smaller secondary mirror. They have the eyepiece at the front and a tube that is open. The mirrors mean that the tube can be shorter.
Typically they come with finderscopes that help you locate the target object in the sky so you can focus in on it.
Newtonian reflectors (including Dobsonians) are popular telescopes for home use.
They are better for viewing galaxies.
Disadvantages of reflector telescopes:
- The image is reflected upside-down (I wrote about why and how it’s solved), e.g., a correction piece will turn it right side up.
- Aberrations (other than chromatic) and contrast issues
- They do need regular collimation and cleaning. So they require more maintenance than refractors.
Video: difference between a reflector and a Refractor Telescope
If you prefer a video to explain…
Are refactors better than reflectors?
In some respects a refractor telescope is better then a reflector. With the same aperture size, they give brighter and higher resolution images.
They are good for viewing the planets and the moon. But also double for terrestrial viewing.
They are better for traveling. Being lightweight refractors are an ideal choice for travelers, wanting something portable, and for children.
But, size wise, they are limited by lens sag, which becomes an issue with increasing size.
Why are reflectors better than refractors?
Reflectors can be built to gather more light than refractors. They are better suited for viewing deep sky objects, such as galaxies and are more versatile.
Final Thoughts about choosing reflector or refractor
At the end of the day, whether you choose a reflector or refractor depends on what you intend using your telescope for, your budget, and whether you can physically manage the scope (where will you store it or do you need to transport it. All of the telescope types have their advantages and disadvantages.
NASA On Telescopes | Space Place |
Main image credits: ID 2306640 © Njnightsky and ID 169501910 © Johnypan | Dreamstime.com