Looking to buy a new telescope? Or perhaps you’ve recently got one, and you need essential accessories? Buying a scope and the appropriate accessories can seem like a daunting task. Where do you start?
Here are a few pointers.
In order to know what kind of telescope you’d like to buy, it’s important to consider a few questions: What do you want to observe with it — just the Moon and planets, or do you want to see fainter deep-sky objects? Do you need something light that you can take with you to the cottage? And do you want to photograph celestial objects with it?
Let’s look at the important things you need to know about telescopes.
First is the aperture. This is the diameter of its main lens or mirror. Typically, aperture is expressed in millimetres or, for larger telescopes, in inches. Basically, the bigger the aperture, the more light-gathering potential, letting you see fainter objects.
Comparing the light-gathering power of two telescopes is done by calculating by the ratio of their diameters squared. Let’s work through an example.
For a 6-inch telescope, the diameter squared is 6 × 6 = 36. For an 11-inch (279.4-mm) telescope, the diameter squared is 11 × 11 = 121.
The ratio between the two numbers is 121 ÷ 36 = 3.36, so an 11-inch telescope gathers more than three times more light than 6-inch telescope. A 6-inch telescope performs 2.25 times better than a four-inch telescope.
The downside is that a larger aperture means a bigger telescope. If you’re an urban dweller, it is more cumbersome to drag a large telescope outside the city — and if it’s more cumbersome, chances are you’re less likely to set it up.
Eyepieces are very important. Each eyepiece delivers a particular amount of magnification, so most people buy a range of focal lengths (that’s the little number labelled on the eyepiece). Don’t get hung up about extreme magnifying powers, like 500x. Due to the turbulence of Earth’s atmosphere all telescopes have a limiting useful magnification that is 50 times its aperture in inches, or twice its aperture in millimetres.
Different types of telescopes
The main types of telescopes each have their advantages.
Refractors have a lens at the front that forms an image at the back. These tend to be cheaper owing to their simple design. They are best for planetary and lunar observing because their smaller apertures work best on bright objects, and they are lighter and more portable than other types. The minimum aperture I recommend is 70mm to 80mm.
Reflector telescopes use mirrors to gather and focus the light from incoming objects and direct it out the side of the tube. This type tends to have larger apertures, making them good for viewing dimmer deep-sky objects like star clusters, nebulas and galaxies. The minimum aperture I recommend is six or eight inches. Although larger sizes are quite affordable, those ones can be very large and heavy. Dobsonian telescopes are reflectors that are mounted on a swivelling box instead of a tripod, making them especially sturdy and easy to use.
The Schmidt-Cassegrain telescope is the most compact type. Called a Schmidt-Cass or SCT for short, it uses both lenses and mirrors to form an image in a much shorter tube. This makes them easier to transport, but more expensive. Common apertures for SCTs are in the six-inch to eight-inch range, but smaller and larger sizes are available.
All three telescope types come in manual versions that you point by hand, or as motorized GoTo systems that are computerized, and you can pick targets from a database in the handset. You’ll need to supply power to the latter. For either type, the sturdier the tripod the better, so the view doesn’t shake too much when you focus the telescope.
My first telescope was a simple refractor, and although it was wonderful (even more so after I upgraded it), the next one I moved to was a 6-inch Celestron NexStar Schmidt-Cassegrain telescope. It was compact, easy to set up on my back deck or transport to a dark-sky site.
But then I wanted more. I wanted to take images of the night sky, be it the Moon, planets or deep-sky objects. But this takes a lot more work and a special kind of mount — the structure on which the telescope sits.
Rather than a simple alt-azimuth mount, which allows you to move the telescope left-right horizontally and up-down in elevation (altitude), imaging needs a sturdy motorized equatorial mount which you align with the North Celestial Pole, near Polaris (the North Star). This allows the telescope to follow the target as Earth rotates, keeping whatever you’re observing perfectly still. Alignment can be tricky. Personally, it took me more than a year to learn this, but I’m fairly sure I just didn’t grasp the concept. Equatorial mounts are also a lot heavier, and you need weights to balance the telescope and camera for smooth tracking.
When you are ready to buy a telescope, consider purchasing from a local astronomy retailer, rather than Amazon or a department store. They’ll be able to help you select the best model for your budget and experience level, as well as suitable eyepieces and accessories.
Using your telescope
Next step: How do you use your new telescope?
I’m not big on reading manuals, but you should. It will help immensely; I know it helped me.
As well, you can always do a search on YouTube for the type of telescope you own to gain some pointers. I’ve found this incredibly helpful.
Another quick tip is, after COVID-19 is over and done with, try to attend a star party. Ask people about their telescopes. Most of them will be happy to share their experiences and a glimpse through their telescopes.
Once you have your telescope, master it and improve your knowledge by exploring on clear nights. I learned to navigate the night sky using my GoTo telescope by just slewing it around the sky. The first thing I found on my own was the Ring Nebula (Messier 57) using a good sky chart.
It might seem like a lot, but don’t be intimidated when it comes to buying a telescope. Ask telescope owners, join a Facebook group or reach out to a telescope or astronomy community. Most people are happy to help and share their experiences. After all, we’re all looking for the same thing: a wonderful view of the night sky and all the universe has to offer.