Image credit: ORION Collaborative Super Telescope (OCST) - M42 Orion Nebula

Which Telescope Should You Buy to Start Stargazing?Article by Morgan Nathan ('Storm")

Hello! My name is Morgan but you can call me Storm, and within this article, I will be going in depth into all the different types of telescopes, the advantages and disadvantages of each type, and which one you should buy!

Firstly I'm going to start off by saying, if you want to take good images through your telescope (like the one at the top of this page) then you have to be prepared to spend a little more than you are probably expecting. However, if you are only wanting to look through it and not take high-quality pictures, you can get away with a much cheaper option.

Following on, also keep in mind that what defines a good telescope isnt how much 'zoom' it has, more as the quality of it determines it as such.

Lets talk about the 3 main types of telescopes, you have refractor telescopes, which most people are familiar with, and you have reflector telescopes. Both options having few sub-types. And the last, a composite, also called a compound telescope, which is a hybrid of both refractor and reflector telescopes!

Refractors

Refractor telescopes are by far the most recognisable and intuitive to use type of telescope. When you say the word "telescope", your mind most likely goes to an image similar to the one directly above.

How do they work?

The pros and cons

As with all things, not everything is perfect and there are always some sort of draw-back(s).

Refractors have 3 major problems:

1.  The way they focus the light. If you look at the lens of a refractor, you can see that it is quite obviously circular shapped, which when circular light gets projected onto a circular surface (your eye), there is no problem. 

But the sensor of most cameras are rectangular (or sometimes square), which, as you should know from your childhood block puzzle, the square doesn't fit into the circular hole. This creates a special type of distortion at the edge of the image called "Field Curve", and this is a major problem for most telescope systems. So you then have to spend an extra amount of money to get a special attachment of glass called a "Field Flattener". This glass corrects the distorted edge and makes the image crisp throughout.

2. The lens size. Refractors use solid pieces of curved glass to magnify the image, which as you would expect, can get very heavy at large sizes. Especially when your refractor has 3 or more lenses. So if you want a large refractor, you'll need a powerful tracking mount to do along with it.

3. Chromatic Aberration. Although the name may sound scary, it is a fundamental part of the telescope. Chromatic aberration is caused when the lenses are not focusing all of the light evenly. If you think about white light, you can recreate it on a screen with 3 colours; red, green, and blue. Most refractors have a lens to focus the red/yellow and a lens to focus the green/violet light, they only pick 2 lenses to do this, meaning the blue colours are left out. This causes a unique 'halo' around the stars and objects in the image. We call this Chromatic aberration.

But some higher-end refractors have 3 or more lenses, meaning all red/yellow, green/violet, and blue/dark-blue colours are in focus and sharp. Meaning the final image will appear cleaner, crisper, and sharper. But this comes at an extra cost, we call these refractors with 3 lenses triplets.

I mentioned how some have 3 or more lenses, so you may be wondering what this 'or more' is. Well, earlier I mentioned the field curvature and distortion, and without buying a field flattener, some refractors come with a flattening lens already built into it.

Reflectors

In my own personal opinion, reflectors are arguably the best type of telescope. While they are less intuitive to use, they can provide sharper, and closer magnifications on a particular target for a much more affordable price tag.

How do they work?

The method of how different reflector telescopes magnify light is largely the same, but with some small key differences.

The most well-known type of reflector is the Newtonian, as the name suggests, it was invented by Isaac Newton in 1668. They work by bending the incoming light on a curved mirror, reflecting it forward into the flat secondary mirror, which then directs the light into the camera/observer's eye. The diameter of the first mirror (the primary mirror) determines how much light it will pull in, and the distance from the primary to the secondary determines how much 'zoom' the telescope has. Newtonians can also come in a ground-mounted variant called a "Dobsonian".

Advantages and disadvantages

Yet again, we are met with some perticular problems with these sort of telescopes. They have 3 main issues as well:

1. Weight. While reflectors are cheaper and more light-weight than refractors, they beg for larger apertures (M1 in the diagram above). This in turn adds a lot of extra weight. So you will need a strong tracking mount to support these giant sizes.

2. Collimation. Collimation is the process of aligning the two mirrors. This can be a tedious task, especially with long focal lengths (red arrows in diagram above).

3. Comatic aberration. Similar to Chromatic Aberration for refractors, reflectors have an issue where stars in the image can appear elongated and oddly shapped. But following exact to refractors, you are able to buy correctors for this distortion. But this is where Ritchey Chrétien telescopes come into play. Due to the hyberbolic primary and secondary mirrors, this comatic aberration (coma for short) is practically eliminated entirely, making it a perfect choice for low-maintenance telescopes (aka space telescopes).

Composite/compound Telescopes

They have no Chromatic or Comatic aberration, they have a flat field, they rarely need collimation. What more could you want? Well, not all things are as perfect as they seem. Compound telescopes have some minor drawbacks which make them highly unrecommended to beginner stargazers. Namely being:

1. They are incredibly heavy. Compound telescopes are very heavy. And just like reflectors, they demand for large apertures to make them useful.

2. Long focal length. Because of the internal design, compound telescopes focus the light over an extremely long distance, this makes them less efficient at transferring the light to the camera sensor, which is why you need such large apertures. And due to the long focal length, they have a lot of 'zoom', so they are hard to point accurately in the sky, yet another problem for beginner stargazers.

Summary

To complete this long-winded explanation of the main types of telescopes. I want to wrap this all up by mentioning the key points of each telescope design:

Refractors:

• Are easy to use

• Intuitive

• Have some optical flaws

Reflectors:

• Good at getting close-up views of planets and stars

• Need colimation if used for taking images

• Can be light weight, but quickly gain weight with size

Compound/composite:

• Perfect for hard-core astrophotographers shooting for galaxies and small nebulae

• Corrects images nicely

• Heavy and cumbersome

So which one should you buy?

In general, reflectors only come in one flavor, which to say means they are simple and (mostly) inexpensive.

Furthermore, reflectors can be widely used and can quickly learnt how to use.

And if you are just starting out, I highly do not recommend buying a compound/composite telescope due to their harsh nature in size and weight as well as the problem of pointing accuracy.

So in conclusion, I personally can say that nothing will beat what a 8" (eight inch) dobsonian/newtonian can provide. They are easy to use, and can show people the stars, planets, and moon all in esquisite detail. All for a rather cheap price that won't leave you digging deep into your pockets!