Green Witch
  BRIEF OVERVIEW

Welcome to Green Witch, one of the UK's leading astronomy shops. Our background is in professional astronomy but are also amateur astronomers willing to share our knowledge with you.

We offer free, friendly advice and all the support you need to get the best from your purchase. We recognise the needs of beginners and will help you choose and use the equipment that is right for you.

We are also nature enthusiasts and our experise in fine optics enables us to offer an excellent service to bird watchers and nature lovers as well.

We have a well-stocked showroom where you are welcome to try out binoculars and field scopes before buying. We are usually open six days a week from 10 until 5 and do not close for lunch. You are welcome to call in to browse, buy or seek advice. Please phone for an appointment.

Check out our web site where you can order online, or phone us for advice and mail order.

 

 

TELESCOPES
Click here to bookmark this page

Click here to skip the blurb and go straight to our online shop

The telescopes we supply

We supply all kinds of optical telescopes, for land, sea and sky. In astronomy we cover everything from simple starter telescopes for children, through the full range for amateurs, to large research telescopes. Our staff have extensive backgrounds in professional astronomy as well as being keen amateurs so you can be sure of getting sound advice based on personal experience. But don't be put off if you are a beginner. We know what it is like to get started and how bewildering the choice of equipment can be. We appreciate what it is like to take the first steps into this fascinating hobby.

We also supply a wide range of terrestrial telescopes for bird watching, nature, sport and leisure, both on land and sea. In common with most people we have an interest in nature and regularly use our own equipment to observe and photograph wildlife. We can give advice based on personal experience and help you decide which equipment will meet your needs.

How to Choose a Telescope

Do you want to use your telescope primarily for astronomy or for terrestrial use? Is portability and ruggedness important? There are many factors to consider but let's begin with the intended use. Telescopes fall into two very broad categories, astronomical and terrestrial. Both work on the same principles and have many features in common but tend to be very different in practice.

Astronomical telescopes are used in the main to observe faint objects and need to collect a lot of light. This often makes them big and bulky, and supporting them so that they can point anywhere in the sky and track an object often leads to heavy and complex mounting arrangements. Terrestrial telescopes on the other hand usually need to be portable and rugged; size and weight is also significant.

There is nothing to stop you using an astronomical telescope for terrestrial viewing, and vice versa, but this is often inconvenient and does not work as well as a telescope optimised for the purpose. However, there are some telescopes that work very well for some types of astronomy as well as terrestrial targets and we can advise you on choosing these.

In the next sections we will set out some of the things to bear in mind when choosing a telescope.

Telescopes for Astronomy

If your primary interest is to look at the night sky then the best option is to choose a telescope designed specifically for astronomy. This will offer better value for money and better performance than a terrestrial telescope. If your main use is for bird-watching or other terrestrial interests then you should consider a field scope. These can also be used for astronomy within certain limitations and are dealt with in subsequent sections.

The three most important criteria for a good astronomical telescope are its light-gathering power, the quality of its optics and the mounting. In addition you will want to consider portability, where you will keep and use the telescope, and, of course, the price.

Light-gathering Power

With a few exceptions, all the objects you will want to observe in the sky will be very faint so the ability of the telescope to collect as much light as possible is important. This is the reason why astronomical telescopes tend to be bigger and bulkier than their terrestrial counterparts. Telescopes can be divided into three main types depending on how they collect and focus the light. The first type use a lens and are called refractors; the second type use a mirror and are called reflectors; the third type use a combination of mirrors and lenses and are called catadioptrics. Each type has its own advantages and disadvantages but all types can be used for general astronomy.

Reflectors generally provide the greatest light-gathering power for a given amount of money and are often the preferred choice when viewing faint deep-space objects such as galaxies and nebulae (dust clouds). Refractors are often preferred for planetary observation where good contrast and the ability to show fine details are more important than light-gathering power. Catadioptrics are often the most compact telescopes and are becoming increasingly popular, especially with built-in computer control.

Optical Quality

This is perhaps the hardest factor for a beginner to assess, but it is extremely important. In general terms, the more you pay the better the optics are likely to be, but this is only true when buying quality brands from specialist retailers. More expensive telescopes tend to be purchased by experienced users who know how to assess quality so there is little opportunity for poor quality products to make an impact in the higher price ranges. Unfortunately, in the lower price ranges where most people start, there are lots of poor quality products around. These often attract first-time buyers because they are widely available. This is a pity because the disappointing results can put people off for good.

Many of the poorer quality telescopes are sold through department stores, catalogue shops and other non-specialist retailers. These telescopes offer the retailer better profit margins than the quality brands, and this can only be achieved by higher prices or cheaper-quality products.

So how do you ensure you will get the quality of optics you need? The best way is to discuss your requirements with a reputable supplier. His or her aim should be to help you choose the telescope that is best for you within your budget. If you don't feel you are getting good advice, or aren't confident that the sales assistant knows the subject well, then try somewhere else. You can also get good advice from your local astronomy club. These are generally friendly places where people are only too happy to discuss the merits of different makes and models. Try to talk to several people and avoid taking the advice of someone who thinks the only good telescope is the one that he or she owns. It may not be the right one for you.

Mounting

Telescope mounts come in many different forms but can be grouped into two main types, alt-azimuth and equatorial. Both have two axes to rotate the telescope around. In an alt-azimuth mount the main axis is vertical but in an equatorial mount the main axis is tilted over to be parallel to the Earth's axis of rotation. Alt-azimuth mounts are simpler and cheaper; equatorial mounts are easier to use for tracking objects. (But see the section on Computer Control)

If your interest is very casual and you only want to look at the Moon and perhaps see the Galilean moons around Jupiter and Saturn's rings, then you may want to consider a very simple and inexpensive telescope on a light-weight alt-azimuth mount.

For more serious use an equatorial mount is much easier to use, although at first sight it looks more complicated. These mounts are often fitted with slow-motion controls which are very convenient for making small adjustments, particularly at high magnifications.

One type of alt-azimuth mount deserves a special mention. This is the Dobsonian mount which has become very popular in recent years, particularly for home-built telescopes. It is designed to be used with reflecting telescopes and is very cost-effective for larger ones. Many home-builders are happy to swap ease of use for its low cost.

Portability

As we mentioned above, astronomical telescopes can be big and bulky so you need to consider where you will keep yours and how easy it will be to get it out. Remember the old maxim that "a small telescope outdoors collects more light than a big one in the cupboard". This is one area where the catadioptrics provide an advantage. Their combination of mirrors and lenses tends to produce more compact packages that are easier to handle.

The best way to assess whether a telescope will be manageable is to see it for yourself and feel the weight. This is where a specialist retailer with a good selection of different telescopes can provide invaluable assistance.

If you plan to have a permanent installation you will be able to cope with a larger telescope, but if, like most people, you will need to get the telescope out when you want to use it, make sure you can handle it safely and comfortably, preferably by yourself. If it requires two people to handle the telescope you will find that it doesn't get used as often.

There are several highly-portable telescopes available which have excellent optical performance and are well-worth considering. Some of them can be carried conveniently on holiday and are small enough to travel as cabin baggage.

If you live in an area with a lot of background light from street lights, or your view is severely restricted by trees or buildings then you may want to consider a telescope that will be easy to transport to a better site. Choose something that will travel comfortably in your car. If you have to travel by public transport then an ultra-portable may be more appropriate.

Computer Control

Computer-controlled mounts are widely available, even on entry-level telescopes. They are proving very popular, particularly with beginners who value the help that computer control provides. It is like having a friendly expert alongside you to help find objects and show you where in the sky they are. Also, many of the computer controllers contain information about the objects which they will display for you while you are observing.

Computer control does not usually involve linking your telescope to a PC. Most computer control systems consist of a small handset linked to the telescope by a short cable. Motors and encoders are either built into the mount or are attached to it, making the telescope self-contained. Power is usually supplied by batteries (most commonly 12 volts) but cables to connect to car cigarette lighters and mains power supplies are also available. If you plan to use a mains power supply, remember that things get damp outdoors at night so make sure your supply is suitable for this. At the very least you must use it with an earth-leakage circuit breaker and protect it from the damp. A better alternative is to use a rechargeable battery pack. Neat units that will power your telescope for several nights are available with cigarette lighter sockets.

Most computer-controlled telescopes for beginners come with alt-azimuth mounts. These are lighter and easier to set up than equatorial mounts. In the section on mounts we said that equatorial mounts are easier to use, but with a computer to handle the tracking, the alt-az is easier.

Because it is light and compact, the alt-az mount is often coupled with a compact telescope tube. Good examples are the ETX range from Meade and the NexStar range from Celestron. Most of these are catadioptric telescopes but both manufacturers also offer short-tube refractors on computer-controlled mounts. These are particularly suitable for beginners and have many of the advantages of large binoculars without the disadvantages.

Price

When you consider the quality of the optics in good astronomical telescopes and the amount of engineering going into them they represent very good value for money. With prices starting around 100 there is something to suit most pockets. But how much do you need to pay?

When I first wrote this web page I included some price ranges for guidance but telescope prices have fallen so rapidly it soon got out of date. For example, a four-inch refractor on a sturdy equatorial mount now costs less than 300 compared with over 500 just a few years ago.

Our on-line catalogue shows a wide range of telescopes and we recommend you browse through it to get an idea of what is available. Within the catalogue we have identified some of the more popular telescopes which you may find helpful in narrowing the range of choices.

Telescopes for Terrestrial Use

Almost all terrestrial telescopes use lenses to form the image. You may come across specialist ones that use mirrors but these are rare so I'll confine my remarks to 'normal' field scopes using lenses.

Optical quality, size, weight and price are the main criteria to consider when choosing a field scope, but other factors such as waterproofing and magnification need to be considered at the time of buying. Astronomical telescopes invariably have interchangeable eyepieces allowing any magnification to be selected but field scopes may come with a fixed eyepiece that can't be interchanged, or a limited range of eyepieces to choose from. Zoom eyepieces which allow a range of magnifications are much more common in field scopes than in astronomy. More expensive telescopes are often sold as separate bodies and eyepieces allowing you to choose the eyepiece you prefer. Less expensive packages often come with a fixed eyepiece, but this is often a zoom giving you a range of magnification.

Aperture - the size of the light-gathering lens

The larger the aperture the higher the magnification you can use in any particular lighting conditions. The most common choices are around 50mm, 60-70mm and 80mm although you will find larger ones occasionally. 60-70mm is perhaps the most popular, offering a good balance between aperture, size and weight.

Choice of Eyepiece

Purists will probably opt for a fixed magnification eyepiece, or a set of interchangeable ones, arguing that the image quality will be better than in a zoom eyepiece. However, modern zooms are very good and are the first choice for most people. Zoom range is usually 3 to 1, e.g. 16-48x or 20-60x. The same eyepiece may be usable with different size telescopes in a range. It will usually give different magnifications in the different sizes of telescopes.

Eyepiece quality varies considerably and a higher price usually means better quality although we recommend trying the eyepiece and telescope before buying to make sure you are happy with their performance.

Size and Weight

Bigger telescopes usually weigh more than small ones but weight is affected by the materials used. If the telescope is to be used at home or carried only small distances then weight may not be too important. But if you plan to trudge around the countryside with it all day then weight may be one of the main considerations.

Quality of the Objective Lens

The objective is the large lens at the front of the body that collects and focuses the light to form the image that you examine through the eyepiece. Its quality is the main factor in determining optical performance (although a poor eyepiece will cancel any advantage that an excellent objective provides). All lenses cause white light to be dispersed into its component colours because all wavelengths are refracted by different degrees. Single-lens objectives produce poor images with lots of colour aberrations and you will not find them in anything other than a cheap child's telescope. All field scopes use two or more lenses working together to form the objective. They may be cemented together or have an air gap between them but they will always be of different materials with different characteristics.

An objective made of two pieces of glass is usually referred to as 'achromatic' meaning that it is free of any false colour. It won't be quite free and you will notice coloured tinges at the edges of objects, especially when viewed against a light background such as the sky. Lenses that do a better job of colour correcting are referred to as 'apochromatic' and you will hear people talking about an 'apo' or 'apos'. Apochromats usually require three lenses in the objective but there is no hard and fast specification so you will encounter manufacturers using two lenses made of exotic materials and calling them apochromats.

Terms that are often associated with the more exotic glasses are 'fluorite' and 'ED'. Without going into any detail it is sufficient to say that the use of these glasses is intended to give better performance and will usually cost more. Often a manufacturer will offer a standard telescope and an ED version. Try both and see if you can see the difference. If not, opt for the cheaper alternative.

Angled or Straight?

These terms refer to the way the eyepiece is attached to the body, i.e. sticking up at an angle of (usually) 45 degrees or coming straight out of the back. The more popular form is angled because looking down at a slight angle is more comfortable, especially when sitting. Also, the telescope is lower than a straight one would be and this means the tripod doesn't need to be so high and will be more stable. However, straight is preferred by some people who find it easier to locate things quickly if their eyes are pointing in the same direction as the telescope.

Waterproof and Nitrogen Filling

If you plan to use your telescope in wet or very cold conditions you should look for one that is waterproof. These are often described as being 'nitrogen filled' but nitrogen filling does not guarantee that the telescope is waterproof. Check the specification if this is important to you.

Manufacturers fill telescopes with nitrogen gas before sealing the tube because it can be produced cheaply in a very dry form. It is also inert and will not cause problems if it leaks. If the inside of the tube is not extremely dry then the optics will tend to fog up in cold conditions.

Other considerations

Can the telescope be attached to a tripod? Almost certainly yes, but if you choose an old-fashioned draw-tube telescope because you want to look like Nelson it probably won't have a tripod fitting.

Does the manufacturer provide a convenient method of attaching a camera? Digiscoping is becoming increasingly popular and you may want to use your telescope as a telephoto lens. Most manufacturers recognise this but some have better solutions than others.

Is a case available for the telescope? A stay-on case is quite important if the telescope is to be used under arduous conditions. Most manufacturers provide them as optional extras and there are specialist companies such as Skua who make third-party cases. You should be able to get one for almost any scope but it's wise to check.

Will my camera tripod be suitable? It depends on the the tripod and the telescope. Almost certainly it will fit as the standard quarter inch screw fitting is virtually universal. But whether it will be effective is another matter. If the telescope is heavy and you want to use it at high magnification then a light tripod will not be stable enough. If the telescope is wobbling it doesn't matter how good the optics are you will not enjoy the experience. If you hope to use your existing tripod then take it along when you go to buy a telescope. You will soon see if it is suitable.

In this short guide I've tried to cover the important issues to consider but please contact us if you have any questions or don't understand anything I've said. Our online catalogue contains a wide range of telescopes from leading manufacturers so I recommend you browse through it then call us or visit us for advice.

Would you like to buy a telescope?

Click here for more information or to buy a telescope from our online shop


| Astrolabes | Bats | CCD Cameras | Celestron | Hawke | Hyperstar | Microscopes | Takahashi | Telescopes |
   BUY A TELESCOPE

Telescopes Click here to buy telescopes from our online shop