INTRODUCTION TO ASTRONOMY

This article featured in the March 2003 Beginners Magazine

MORE ABOUT TELESCOPES

5. WHICH TELESCOPE TO BUY

In the previous articles in this series we considered the first step for the astronomy beginner to take, this was to buy a book with sky maps and become familiar with the night sky. The second was a look at binoculars as the first instrument needed to improve the view of the night sky. In the third article the two main types of telescopes were explained these are the refractor and reflector. The last article looked at how the telescope works.

In this article we what to look for when buying a telescope. In future articles advice will be given on how to use an astronomical telescope and how to get the best out of it.

The first consideration is of course how much can be afforded to spend on a telescope. Like all hobbies, there is always some cost involved and the cost generally follows the depth into which the hobby is pursued. To buy a telescope which is able to return useful views of the interesting objects, other than the Moon and brighter planets, upwards of £200 will need to be spent. Like all things you do get what you pay for with a telescope.

In considering buying a telescope we will be looking at a new instrument bought from a respectable supplier but by purchasing an instrument second hand the price may be reduced by between a third and a half of the RRP. Many second hand instruments are advertised in monthly magazines such as Astronomy Now.

Telescopes come in all shapes, sizes, designs and prices so we must first consider what we are going to use the telescope for. For a first telescope that is going to be used for general observation on a casual basis a 150mm (6 inch) Dobsonian would be a good starting point. This type of instrument is simple, light, easy to use and relatively cheap to buy. One of the cheapest in this range is the Helios Skyliner-150 which can be bought for a little as £229. Other manufacturers produce similar instruments of this type with prices up to about £370 and all are excellent value for money. Most instruments are supplied with two eyepieces and a Barlow Lens that will double the magnification of each eyepiece. A Dobsonian of less than 150mm aperture will be too small to satisfy the appetite of an enthusiastic new astronomer because many of those interesting faint objects, written about in books and magazines will be just out of its reach.

THE HELIOS SKYLINER - 150

The Dobsonian is an excellent telescope for the beginner and will give many years of enjoyment. Many advanced astronomers use their original 150mm telescope as much as their bigger and more powerful later acquisitions because it is so easy to set up and use.

A Dobsonian is an excellent instrument for casual optical observation but photographic work will be limited to views of the Moon and the brighter planets. Only short exposures can be used because the Dobsonian is not usually driven. A power drive system is required to enable the telescope to track stars and other objects as they appear to move across the sky. A special type of mounting is used when it is necessary to track object for more than about 20 to 30 seconds. This type of mounting is known as an Equatorial Mount. One of the two rotational axes is set at an angle to align with the axis of rotation of the Earth. This axis may then be driven using a hand operated knob or a battery driven motor. Both reflecting and refracting telescopes can be fitted to this type of mounting.

As with the Dobsonian the minimum aperture of 150mm for a reflector should be considered or 120mm for a refractor. A telescope of this type is going to have a price tab above £350 and £450 and above for electrically powered models.

TAL 150P £359	EVOSTAR 120 £299

With a slightly larger price tag is a new range of high tech computer controlled telescopes, known as 'goto' telescopes. This type of instrument is a beautiful piece of equipment if the a price tag starting at £600 can be afforded. This type of telescope is supplied with a tripod and a computer handset with a database containing thousands of objects. Once set up level and pointing to north the telescope automatically points to a known star and asks the user to adjust the alignment on to that star. After repeating this for a second star the telescope will automatically find and track any object in its database.

MEADE ETX90E £599

Next month we will start learning how to use some of the telescopes described in this series of articles.

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