If you’re new to astronomy and never had a space telescope before, you may have just discovered that there are different types of telescopes. Each type has differences based not only on its appearance but also on the way it manipulates light.
In short, a refracting telescope uses lenses, whereas a reflecting telescope uses mirrors.
It’s fascinating that we can view terrestrial objects in deep space thanks to a couple of mirrors and lenses. Telescope designs play a big role in the optical performance of these optical instruments, and even in the orientation in which the image is displayed.
Did you know that some types of telescope display images upside-down? This is something you should definitely know if you’re looking to purchase a scope for exciting nights of terrestrial observation!
Read on to learn more about refracting telescopes vs reflecting telescopes and what type of viewing experience they offer stargazers.
What is Reflection?
We have all seen our reflection in objects like mirrors, spoons, and bodies of water, but what causes these surfaces to display an image of ourselves?
It’s all about light!
Light rays can bounce off of surfaces (both smooth and rough), and this is essentially what reflection is. When light bounces off a smooth, shiny surface at the same angle, this results in specular reflection.
When this reflected light enters our eyes, special receptor cells in the eyes process the light rays and send signals to our brain. The brain then uses the signals to create an image, and that’s how we see a reflection.
Reflecting or reflector telescopes use mirrors to reflect light and produce a magnified image.
What is Refraction?
Remember how we explained that light bounces off the surface of objects? Well, light also travels through the surface of transparent objects, as you would know if you’ve ever seen the sun shining through a window.
When light travels through a transparent object that is denser than air (such as water or glass), it is slowed down by each boundary it crosses. This change in the speed of movement causes the light to change direction and appear to bend. This is refraction in a nutshell.
Refracting or refractor telescopes work based on the principle of refraction. These telescopes use convex lenses, which are ideal for refracting light and making objects appear bigger.
So, How Are They Different?
There are several factors used in each type of telescope, besides the principles of optics.
As mentioned above, some optical telescopes come with more than one eyepiece, offering the viewer different magnification options. If not, astronomy enthusiasts have the option of buying their preferred eyepiece.
Don’t be confused by this technical word. Aperture simply refers to the opening at which light enters the telescope.
The diameter of the aperture is usually written in inches or millimetres, and the larger a scope’s aperture is, the more light it lets in. Reflectors tend to have larger apertures than refactors.
This handy device sits on top of the optical tube and helps the viewer locate the celestial body he/she is looking for before viewing it in full magnification. Both types of telescope typically come with finder scopes.
The tube of the telescope houses the lenses and mirrors and makes up the structure of the instrument. Refracting telescopes may have a longer optical tube than reflecting scopes since the focal length of a refractor is directly related to the size of the lens.
Refracting telescopes have two lenses: an objective lens (the largest), which is also the aperture and is found at the front of the scope, and an eyepiece or ocular lens, placed at the other end of the instrument.
The eyepiece attachment on modern telescopes also contains lenses that directly contribute to the magnifying power of the scope.
Reflecting telescopes contain two mirrors. The objective mirror, also called the primary mirror, is the larger of the two and is typically concave (like the inside of a spoon). It sits at the end of the scope that is opposite the aperture.
The secondary mirror is much smaller and can be flat or concave, depending on the type of reflecting telescope. The Cassegrain telescope uses a concave secondary mirror while the Newtonian telescope uses a flat secondary mirror.
Let’s look at the main features of a refracting telescope vs reflecting telescope.
Maintenance and Care
Reflector telescopes usually have to be collimated before use, particularly if the user moves the instrument from one location to another or routinely packs it up after a fun night of astronomical observation.
Collimating a reflector simply means aligning its mirrors correctly to obtain the best view. These mirrors also need regular cleaning as the tube does not seal dust out.
Refractor telescopes, on the other hand, don’t require much maintenance but should of course be cleaned when necessary and stored safely when not in use.
Size and Portability
While both types of telescopes are similar in size, refactors tend to be a bit smaller, lighter, and more compact, making them easier to carry around.
The quality of the image you see when you look through a telescope depends on a few factors like type, size of its aperture, and magnifying power.
Perhaps the biggest difference between the two types of telescopes is that refractive telescopes show images right side up whereas reflective telescopes display images upside down.
As we mentioned above, the larger a scope’s aperture is, the more light it can use. More light means greater image quality when viewing objects in deep space.
A telescope’s magnifying power not only depends on the body but also on the eyepiece.
Modern telescopes have an eyepiece on the side of the optical tube that allows the stargazer to view deep sky objects more clearly.
One great benefit of modern telescopes is that you can buy additional eyepieces if your telescope does not come with the ones you prefer to use.
You may have seen a number followed by “mm” on an eyepiece. This number indicates the focal length of the eyepiece. The lower the number, the higher the magnification of this piece of equipment.
This is the distance between the aperture and the point at which the rays of light converge or meet. The focal length is also written in inches or millimeters and contributes to the overall length of the telescope. The greater the focal length, the more an object can be magnified.
Physical errors in your telescope can cause celestial objects to look somewhat distorted.
These distortions are called aberrations and while they are not guaranteed to occur, there is a likelihood that they will. The most common aberrations include
- Chromatic aberration, which causes blurred, colored edges around objects. This issue only affects refactors, since it is caused by incorrect refraction of light.
In terms of types of lenses, parabolic lenses are better for refractor telescopes because they correct chromatic aberration, but bear in mind that they are more expensive.
- Reflector telescopes use spherical mirrors, which can result in spherical aberration in images. This type of focus problem makes objects appear with a blurry ring around them. This issue can be corrected by parabolic mirrors, which offer the viewer better image quality.
Reflector telescopes are typically more expensive than the refractor type because they use lenses, which cost more to produce than mirrors.
The price also depends on factors like the aperture and quality of the telescope and additional or innovative features it might have.
Which Telescope is Better?
Each type of telescope has its pros and cons, and the best one for you depends on what you want to get out of it.
A newbie or amateur stargazer would not need the size and quality of a telescope that a professional astronomer would require. That being said, there are excellent reflectors and refractors to suit every stargazer’s budget.
Here’s a quick comparison:
- Best for viewing deep-sky objects – Reflector telescopes, particularly Newtonian reflector scopes. Refractor telescopes are ideal for closer celestial objects in the night sky, like our Solar System.
- Bigger Aperture – Reflector telescopes
- Easier to maintain – Refractor telescopes
- Easier to carry around – Refractors
- Usually more affordable – Reflectors
- Best for beginners – Refractors may be the better telescope for newbies to astronomy, given their compactness, ease of use, and maintenance.
Let’s quickly recap the main differences between refractors and reflectors.
A refracting telescope uses mirrors, produces a right-side-up image, it’s easier to maintain, it’s compact and portable, and it’s ideal for viewing closer astronomical objects. On the downside, it typically costs a bit more and its chromatic aberration can be an issue.
On the other hand, a reflecting telescope uses lenses, produces an upside-down image, it’s more affordable, and it’s best suited for viewing deep space objects. Some drawbacks include heavier weight, more maintenance, and spherical aberration.
Now that you’ve seen the key features of each type of telescope, you can decide which one is best for you.