If you are in the market to buy a telescope, the chances are very high that you stumble upon choosing between
- Refractor Telescope or
- Reflector Telescope
This article will walk you through the differences, pros and cons of refractor and reflector telescope for astrophotography.
Refractor telescopes rely on lenses and use the principle of refraction of light to enlarge an object and project the image on the eyepiece. Reflection law of glass is used in the construction of Reflector Telescope.
Refractor Telescope vs Reflector Telescope and Their Differences
There are many substantial differences between Refractor and Reflector telescope. The differences are given below:
|Refractor Telescope||Reflector Telescope|
|Refractor Telescope suffers from chromatic aberration.||No chromatic aberration is seen in reflector telescope.|
|Lens sag is prominent in this type of telescope.||There is no lens sag in Reflector telescope.|
|Image quality is relatively bad compared to reflector telescope.||Very clear and sharp image quality.|
|Relatively harder to mount.||Relatively easier to mount.|
|Less chance of optical misalignment.||Optical misalignment happens frequently.|
|Relatively easy to use.||Relatively complex to use.|
|Very low maintenance is required.||Frequent maintenance is required.|
|Smaller size of the objective.||Larger size of the objective.|
|A bigger Refractor telescope is not feasible.||A bigger Reflector telescope is definitely feasible.|
|A refractor telescope is lighter.||Reflector telescopes are a little bit heavier in weight.|
As the name suggests, refractor telescopes rely on lenses and use the principle of refraction of light to enlarge an object and project the image on the eyepiece. Refractor Telescopes first originated from Europe in the early 1600’s.
The first refractor telescopes used “Galilean Refractor” design. An objective which is made out of a bi-convex lens and an eyepiece which is made out of a bi-concave lens are used to form a magnified image. The main advantage of using Galilean Refractor design is, we get an image which is erect and true in the left or right perception.
But if you pick up a relatively modern Refractor telescope, you will most possibly pick up a telescope constructed using “Keplerian Refractor” design. Keplerian Refractor uses a convex lens in both objective and eyepiece.
Keplerian Refractor design produces an image by using a bi-convex lens objective which has an extended focal length and a bi-convex lens eyepiece which is placed behind the focal plane. As a result, a horizontally and vertically inverted image is produced.
Though an inverted image is produced by the Keplerian Refractor, it is still preferred over Galilean Refractor as a larger apparent field of view is provided by Keplerian Refractor. Keplerian Refractors are also great for novice astronomers and are most commonly used.
Pros Of Using Refracting Telescopes:
- Refracting telescopes are very rugged. After initial alignment, there are very less chances of misalignment of their optical system.
- Refracting telescopes require less maintenance.
- Easy to use.
- Can capture more detailed and stable image than reflecting telescope of the same size.
Cons Of Using Refracting Telescopes:
There are some drawbacks of using refracting telescopes which are stated below.
- Chromatic Aberration.
- Lens Sag.
- Spherical Aberration.
Reflector Telescope was mainly developed by Issac Newton in 1668. Reflection law of glass is used in the construction of Reflector Telescope. Newton’s design still continues to be used widely in the construction of modern reflector telescopes.
A concave mirror is positioned at the beginning of a large tube-shaped housing. The opposite end of the tube is left open to allow light to pass through the housing. A small mirror inclined at a 45-degree gradient is placed inside of the tube. The light is then reflected by the mirror and projected towards the opening on side of the telescope housing which contains a convex lens eyepiece.
There is a limitation to this design. The small mirror upon which light is reflected back to the eyepiece has a tendency to slightly lessen the essential surface area of the objective. But the reduction is very marginal.
Some people may find looking sideways at objects difficult. That is why a distinct method known as “Cassegrain Reflector” is used to project light to the direction of the eyepiece.
Cassegrain Reflector method uses, a small convex non angled mirror. That small convex mirror reflects light back towards the opening in the center of the objective mirror which contains the convex lens eyepiece. As a result, we can observe objects looking at the back of the telescope.
Pros Of Reflector Telescope:
- Produced image is free from Chromatic Aberration
- Lens sag problem is non-existential in Reflector telescope
- Because of having a larger objective, more light can be captured by reflector telescope. As a result, dimmer objects can be observed with more details and sharpness.
Cons Of Reflector Telescope:
Though reflector telescopes are really good at what they do, there are a few cons.
- As reflector telescope can easily be upscaled in size, the mirrors inside the telescope have to be cleaned because of their open construction.
- Optics can get misaligned easily
- Requires more maintenance
- Relatively hard to use as optics may require frequent alignment
Refractor Telescope Or Reflective Telescope Which One Is Better?
As we learned earlier, refractor telescopes suffer from chromatic aberration and lens sag problem. But Reflector telescopes do not suffer from any of these problems. And the picture quality is better on the reflector telescope thanks to the larger size of its objective.
Reflector telescopes dodge the chromatic aberration problem because of using a convex mirror as objective. And as mirrors can be supported from behind, they do not suffer from the sag problem as refractor telescope does. As a result, reflective telescopes can be much larger in size than refractor telescopes.
The production of a reflector telescope is much cheaper than a refractor telescope. Besides reflector telescopes are also easier to mount because the back of the mirror can be used to attach to the mount.
So we can conclude that reflector telescopes definitely have an upper hand over the refractive telescope. Mainly because most of the problems faced by the refractor telescope can be solved by using the reflector telescope.
If you are looking for a telescope to use professionally, a reflector telescope is the one you should go with. As they can capture more light and can provide superior image quality over the refractor telescope.
And if you are a hobbyist, a refractor telescope is the perfect type of telescope for you. Because they can be compact and are much easier to maintain compared to reflector telescope.