Part 1 dealt with where to look for a telescope and what to expect regarding the spending possibilities. Part 2 will briefly go over the important aspects of a telescope, the types, and where they are on the pricing spectrum.
Most Important Aspects
Aperture – Light Gathering Power
The aperture is the number one thing a telescope must have. How much light the telescope can collect not only determines how bright an object looks, but how well you can resolve finer details. A good backyard telescope has apertures between 80 mm (3.5 inches) to 300 mm (12 inches) or more. With the moon and planets, the larger telescopes will show finer detail than the smaller telescopes, while a deep sky object will appear much brighter and show more contrast than they do on smaller telescopes.
Focal Length – How the Image Appears
The focal length determines how wide or narrow your field of view is, and it also determines your magnification factors when using certain eyepieces. Shorter focal lengths allow wider views in your field of view, thus you see more of the sky, while longer focal lengths give a narrower field of view.
Magnification – How Close Can You Get?
The magnification comes from the eyepieces and lenses you’re using, not from the telescope itself. However, the telescope does determine how much you can.
The higher the aperture, the more you can theoretically magnify. The rule of thumb is 50 times the aperture in inches, or twice the aperture in millimeters. For example, a 100 mm (4 inch) telescope can only go as high as 200x.
Magnification is determined by the focal length of the telescope divided by the eyepiece. A 10 mm eyepiece being used with a 500 mm telescope wields 50 x magnification, while the same eyepiece in a 1000 mm telescope wields 100 x.
The Three Types
- Refractor – uses lenses. They are low maintenance, tend to be smaller and very light weight, hence they are very portable. They also give you sharper images. However, it costs more to make a glass lens than a mirror, so once you get into large refractors, there is a huge spike in prices.
- Reflector – uses mirrors. They are capable of being wider, hence gathering more light, and are much cheaper than refractors with the same aparture, hence you get more bang for your buck. Some cons are that they require a bit of maintenance and care to keep working properly.
- Catadioptric – uses both. You get the best of both worlds – long focal length and wide aperture in a compact size. But their main downside is because of how complex they are made, they can be on the expensive side, especially when we go into the larger Schmidt-Cassegrain telescopes.
Where to Start For Beginners
A beginner’s telescope should be just big enough to collect the light needed to see the details on objects, but they should also be portable enough to easily set up and transport. Essentially, we want to get the most out of our dollars for the first time, and then upgrade to bigger and better telescopes later.
100 mm, or about 4 inches, is a good aperture to start. They can resolve details on the moon and planets, plus showcase some of the brighter deep sky objects.
But what’s the cost?
100 mm refractors usually go for about $4-500 on average, as their prices spike with the size and quality of the lens. But I have seen 100 mm refractors in the $200 range that have shorter focal lengths – they are often advertised as “travel scopes” and sometimes come with a backpack!
100 mm catadioptric telescopes will also be above $300 on average.
100 mm reflectors on the other hand will usually average around $150-200 at their lowest! You can even get a 150 mm reflector (6 inches) for the same price as a 100 mm refractor!
So because of this, I personally recommend getting a 4 inch reflector as your first beginner’s telescope!
However, you must understand that these prices are usually for telescopes that don’t have special mounts, higher quality eye pieces, Barlow lenses, special filters, nor include anything electronic that can be added to it.
We will go over those components to consider in Part 3!