How to Use a Telescope

Astronomy can quickly turn into a very moreish hobby. You start off lying outside on a blanket watching the stars, and before you know it you are purchasing your first telescope and building a dome for it!

How to Use a Telescope

OK, that is a bit overboard, but the prospect of getting a telescope for this starry journey is certainly an exciting one. Yet, all too often people lose their interest in amateur astronomy not long after buying their first telescope. Most telescopes end up unused and dusty, lying in some attic or garage for years before it is pawned. And the single largest reason why this happens? Many beginners simply do not know how to use a telescope correctly.

This short but effective guide is going to turn that all around, so telescopes out and let’s get viewing!

What to Expect

You can get the highest quality and biggest telescope for amateur astronomy, and still be disappointed by what you see. Astronomy magazines have caused some majorly unrealistic expectations! Those wonderful pictures of colourful nebula and seemingly infinite points of lights in globular clusters will be nothing like what you see through your telescope. Even the way planets look in magazines will be a far cry for the real telescopic views.

That is because these photographs are taken by space agencies with the resources and technology none of us ordinary folk could ever dream of owning.

Bummer, right? Not at all! What you actually will see of the Moon, planets, and the brighter clusters, nebula and galaxies will still be absolutely breath-taking once you have busted the unrealistic expectations.

Setting Up

Telescopes take time and practise to learn how to set up properly. A lot of people do not realize this, and so easily become frustrated and discouraged before they have even begun. However, once you have the basics down it will start becoming second nature.

There are a few things to consider when setting up, and some of these points will depend on what type of telescope you have, and the type of mount you own.

Essentially, there are two types of telescopes: refractors and reflectors (as well as hybrids of the two). Refractors use lenses as their main optics whereas reflectors use mirrors. See here if you would like to understand more about reflectors vs. refractors.

Here are some key tips to having a good set up.

The Finderscope

The finderscope is the mini-telescope looking lens on the actual telescope. The finderscope is exactly as advertised: you use this eyepiece to be able to pinpoint the celestial objects you want to view in the actual telescope.

Field of view – a window of how much you can see at any given moment – is quite small in a telescope. This makes it difficult to find objects by looking through your telescope alone, even if you are searching for bigger objects like the Moon or Jupiter!

The finderscope is the solution to this. It doesn’t magnify an object, or the magnification is very low, therefore its field of view is greater (more about this under the section on focal length and magnification). Once you get an object centred in your finderscope, you will be able to see the same object through your telescope, but magnified and in greater detail.

You need to align your telescope and finderscope first.

It is best to do this during the day. Choose a fixed object that doesn’t move and is about a quarter to half a mile away. A chimney or a street light is ideal. Look through your finderscope to locate the object. Note: the image is inverted on some types of finderscopes. Then centre the object in your finderscope by adjusting its screws. Check that you are seeing the same image in the telescope. Now your finderscope is aligned.

Mounting

The two most common types of mounts are alt-azimuth mounts and equatorial mounts.

Alt-azimuth mounts move in an East-West and up-down motion. An alt-azimuth mount is very straightforward to set-up: you just mount your telescope on it and off you go! That is one of the advantages to using these types of mounts. On the other hand, this motion becomes nearly impractical when trying to observe near or at the zenith (the point directly overhead).

As the Earth rotates, the stars have the appearance of moving along the sky at an angle (because the Earth rotates at an angle of 23.5 degrees). Equatorial mounts compensate for this movement. There are parts of sky that are ‘fixed’ – that don’t follow this movement. They are the poles. An equatorial mount has it’s bearings on the North Pole.

Equatorial mounts take a little more understanding and practise to familiarize yourself with. This is because you have to align it to the Pole and to match your geographical location before you can use it properly. They are well worth it, however, because of the accuracy and ease with which you can track the sky. If you ever get into astrophotography, an equatorial mount is a necessity.

Here is a detailed, easy to follow guide on how to properly polar align your equatorial mount.

Collimate

As mentioned earlier, reflectors use mirrors for optics. There are two mirrors, a secondary and a primary. Bumps and handling the telescope can cause these mirrors to move out of alignment, which will in turn produce images that are not focused.

Realigning your optics is called collimating the telescope. It is essential to know how to collimate a telescope if you own a reflector. It seems daunting at first, but as with everything, once you know how and get a little practise in it becomes easier. See this guide for understanding how to align your reflector telescope.

All about Eyepieces

Eyepiece three types
Your telescope would not be much without its lenses. They help magnify and produce detail in the objects you are viewing. Unfortunately, a lot of telescopes – even good telescopes – come with poor quality lenses that you need to replace ASAP if you are serious about your hobby. Thankfully, it is possible to find reasonably priced lenses that will be a good investment.

Focal Length and Magnification

A very basic, non-mathematical explanation of focal length is the distance between the telescopes primary optic and the point where the light rays come together in focus. It is measured in millimetres. Your eyepieces also have a given focal length, which you will find written on them in millimetres.

Understanding this number is important because it is one key piece of information you need to determine how much magnification an eyepiece is able to provide. To calculate the magnification power of an eyepiece, simply divide your telescope’s focal length by that of the eyepiece’s focal length. As an example, you may have a telescope with a focal length of 700 mm. If you use an eyepiece of 25mm, the magnification would be 700/25 = 28 x magnifying power (or simply expressed as 28 power). If you used a lens of smaller focal length, like 7.5mm, you suddenly increase magnifying power: 700/7.5 = 93.9 x power.

There is such a thing as excessive magnification though. You will hardly ever use or need magnifications of over 200, and even then it can be too much depending on what you are viewing. Excessive magnification causes the object to appear much bigger, but without detail. Steer clear of eyepiece marketing ploys advertising 600 x power!

Field of View

Another important number to look at on your eyepiece is its apparent field of view, measured in angles, which expresses how much of the sky ‘fits’ inside the eyepiece. Eyepieces have fields of view ranging from quite narrow (25 – 30 degrees) to very wide (80 degrees or more). Remember though, your eyepiece works together with your telescope. Magnification will affect the apparent field of view, resulting in what is called an actual or true field of view.

Let’s take a telescope with 2000 mm focal length and an eyepiece with a 25mm focal length and 50 degree apparent field of view. We know the magnification would be 2000/25 = 80 x power. Now, the true field of view would be the apparent field of view divided by magnification: 50 / 80 = 0.6 degree. For comparison, the apparent diameter of the full moon is 0.5 degrees.

Low magnification means a larger field of view. Experimenting with lenses to get the perfect balance is key.

As a beginner, you will only really need two very good eyepieces for all your viewing needs. A Barlow lens is a good investment too (it doubles the magnifying power of any eyepiece). Most important when it comes to eyepieces is the quality. Avoid cheap makes, which are usually marked ‘H’ or ‘SR’.

A Brief Look at Filters

Filters can add a whole new dimension to your backyard stargazing experience. Most eyepieces are threaded for filters. Filters work by allowing certain waves of light through and enhancing them, and blocking others out.

There are different filters including Sun and Moon filters, and colour filters for all different types of viewing.

There are even Light Pollution Reduction filters (LPR filters) which block out wavelengths associated with artificial lights.

Maintenance

The last step to using your telescope properly is caring for your telescope. Use will cause the telescope to get a little dirty. Keep your telescope’s lenses or mirrors clean. There are some great guides to this online. There is nothing wrong with having your telescope serviced every now and then!

Store your telescope in a cool, dry place and cover it with light material. Also care for your eyepieces in the same way. This little investment can give you years and years of viewing pleasure when you maintain it properly.

Clear skies, steady seeing, and enjoy!

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