Not sure what telescope to buy? Confused about a refractor vs a reflector telescope. This article will help. It sets out the main differences and the pros and cons for you to weigh up in deciding upon a telescope for you to start using as an amateur astronomer.
How to tell a refractor from a reflector
What’s the difference between a refractor and a reflector?
The obvious one is the location of the eyepiece.
But the main design difference is that reflectors use mirrors and refractors lenses to focus light into image.
But what about performance? Cost? And, how easy are they to use?
|Refractor||Uses a lens|
Eyepiece at rear
Eyepiece at front
Gathers more light
Cleaning of mirrors and tube
Can be subject to dust and humidity
Main Telescope Types Used By Amateur Astronomers
You may come across telescopes described by all different names, which can be confusing. Basically, you can categorize them into three main types.
3 Main Telescope Types (and examples)
These are dioptric, meaning they use refraction. They have convex lenses.
The lens bends or refracts light. Compare this to a reflecting telescope where mirrors reflect light.
These types have the lens at the front and the eyepiece 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.
They are known to suffer from chromatic aberrations, meaning colored fringes around the viewed objects. The other issues are spherical aberrations and lens sag.
Look for telescopes with compound lenses (different types of glass) to correct color aberrations. Doublets are less costly, but triplets are designed to eliminate this issue.
Parabolic lenses correct spherical abberations.
Lens sag becomes a problem with increased size. It only occurs in larger refractors. Here, the lens becomes distorted by its own weight.
For astrophotography, apochromatic refractors are said to be best as they overcome the need for an extra field corrector or space.
These are catoptric, meaning they use reflection.
They use one or more curved mirrors, which makes them free from chromatic aberrations.
Reflectors collect more light than refractors.
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.
Also, as the image is reflected upside-down a finderscope is needed to help locate the object in the sky. Most reflectors come with finderscopes.
Cassegrain reflectors are also used in amateur astronomy.
Reflecting telescopes can suffer from aberrations (other than chromatic) and contrast issues.
They do need regular collimation and cleaning. So they require more maintenance than refractors.
They are better for viewing galaxies.
Cheaper reflectors have spherical mirrors.
Re: Cassegrain Reflectors
A Cassegrain’s primary mirror is parabolic while its secondary is hyperbolic so that it reflects light back through a hole in the primary mirror.
As the name suggests, these telescopes use both lenses and mirrors. There are many variations to these. They include the Maks and the SCTs. My guide on using telescopes to view planets gives the pros and cons of some popular examples of these.
Because of their compact design, the catadioptric telescopes are more portable. Like reflectors, they need collimation, but far less frequently. They can stay aligned and may only need collimation every few years.
These are versatile, being great for deep sky use as well as for viewing planets and the moon.
What is the difference between a reflector and a Refractor Telescope
Watch this video for more detail…
Are refactors better than reflectors?
In some respects they are. With the same aperture size, they give brighter and higher resolution images. Thus, you should get sharper images of stars and better contrast images of planets.
They are good for viewing the planets and the moon.
But, size is limiting with lens sag becoming an issue and these are not preferred by professionals.
Why are reflectors better than refractors?
Reflectors collect more light than refractors.
Reflectors are better for viewing deep sky objects such as galaxies.
While refractors may give clearer views, reflectors are considered more user-friendly.
They are also better on the wallet.
Upkeep Reflectors vs Refractors
The hardest part of the upkeep of a reflector is cleaning the mirror while trying to avoid scratches. Fine scratches even can be worse than dust for messing with views.
Maintaining a reflector involves collimation. The bigger the objective in the reflectors, the greater 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’s involved with collimation? Collimation is the aligning of 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.
At the end of the day, it 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.
Main image credits: ID 2306640 © Njnightsky and ID 169501910 © Johnypan | Dreamstime.com