Advice Choosing A Beginners Telescope

  Introduction

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Choosing a beginners telescope can be daunting; there are different types, sizes of aperture, motorised, non motorised, GoTo, computerised, the choice is vast. Many people commit large cash outlays on a beginners telescope only to see it quickly resold, usually at a loss, or sit gathering dust in a corner. Our aim is to provide unbiased advice and information to enable you to purchase the telescope that meets your requirements, first time!

  Basic Considerations

Your first task is to spend some time thinking about what you want to achieve with your telescopscope, now, in six months, a years time? Do you want to use it occasionally to observe craters on the moon and the larger planets? Or do you intend spending more time finding and observing deeper objects such as nebular, star clusters and galaxies

The next consideration is how you will use the telescope. Are you happy to manually adjust the scope to compensate for the Earths rotation, objects move out of view very quickly at higher magnifications? To find and observe fainter, deeper objects a knowledge of the night sky is essential, but dont let this put you off, this is gained with experience as you climb the learning curve. In other words, you learn by finding one object at a time and adding it to your list. Are you prepared to climb the curve?

Next is location, where do you intend to observe? Are you lucky enough to have reasonably dark skies where you live and an observing area where the telescope can be set-up, or will you have to move the telescope to another location? What means of moving the scope, if this is required, do you have?

The next consideration is budget, how much do you intend spending? Spending a few tens of pounds on a department store telescope will always end in disappointment and is not recommended. This aside, you will need to spend several hundred to several thousand pounds on a beginners telescope depending on your answers to the above questions. Its a good idea to set your budget in advance to avoid overspending on a beginners telescope that is more than you require or can afford.

The answers to these basic questions will determine the type and size of your telescope. The rest of this site will attempt to cover, in more detail, the differences, benefits and limitations of telescopes in general to help you make the right choice. It is strongly recommended that you also read some of the excellent books that have been written on the subject. We have links to what we feel are the best introductions to Astronomy for beginners on this page, for a more complete selection we recommend Best Astronomy Books.

Once you have decided on which telescope is right for you we have some great deals on a selection of recommended Telescopes which we feel are good value all round instruments.

Featured Telescope - Celestron NextStar 102 SLT
As a beginners telescope we would recommend the Celestron NextStar 102 SLT Computerised scope.

NexStar 102SLT - General Features;
  • High quality 102mm refractor
  • Fully computerized altazimuth mount
  • StarPointer finderscope to help with alignment
  • Accurate locating and tracking
  • Quick-release fork arm mount
  • Optical tube and accessory tray
  • Quick no tool set up
  • Sturdy stainless steel tripod
  • Accessory tray included
  • Good for terrestrial and celestial observing
  • Includes NSOL telescope control software for basic control of your telescope via computer (with optional RS-232 cable)

  • PLUS FREE delivery in the UK!

  Focal length

All optical telescopes use an objective, a lens or mirror, to gather, bend and concentrate light from an object. The focal length of an optical system is simply the distance from the objective to the point at which the light converges or focuses.The shorter the focal length, the greater the optical power of the system. Shorter focal lengths will provide less magnified, wider fields of view then systems with longer focal length. Telescopes intended solely for close up lunar or planetary observing therefore, will need longer focal lengths, for wide field views of deep sky objects a shorter focal length is required.

  Aperture Size and Magnification

The aperture of a telescope determines how much light is able to enter the optical system. This is normally measured by the diameter of the objective. As a rule of thumb for astronomy, a three inch lens or a six inch mirror is the smallest you will want to purchase. The larger the aperture the brighter and more detailed the image but, as you might guess, increases in aperture size are usually accompanied by increases in cost, so back to budget considerations. The size of aperture will also determine the overall magnifying power of the system. As a rough guide an optical system will provide fifty times magnification for every inch of aperture. So the department store telescope we spoke of earlier offering six hundred times magnification for a two inch lens is obviously not quite right. Magnifying power is not the critical element to an optical system, much better to have a bright, sharp image that is less magnified than an overpowered, dull and unfocussed image.

  Focal Ratio

The focal ratio of a telescope is determined by dividing the focal length by its aperture size. So an instrument with a focal length of 2032mm and an aperture of 203.2mm or eight inches will have a focal ratio of f10. The focal ratio and therefore the telescope can be termed as fast, medium or slow depending on the ratio. Fast telescopes f3.5 to f6 will provide wider fields of view then medium telescopes of f7 to f11 and slow telescopes of f12 and above, will be provide very narrow fields.

  Types of Telescopes

There are two main types of optical telescopes on the market, refracting or reflecting and these can be further split into a number of sub types.

Refractor telescopes use a convex lens as the objective to gather, bend and focus light at the eye piece. Various configurations of refractor design attempt to correct image orientation and chromatic aberration but the basic principle remains the same. The path light travels through a refractor is demonstrated in the animated graphic below.

Telescopes For Beginners - Refracting Telescopes



Achromatic refractors overcome the need for long focal lengths inherent in refractor design by combining two glass elements to form the objective, these double elements bring two wavelengths of light, usually red and blue, to focus at the same point.

Apochromatic refractors have objectives made from special glass designed to bring three wavelengths of light, usually red, blue and green, to focus at the same point. Apochromatic refractors, or Apo's as they are known, produce very sharp images almost totally free from chromatic aberration, but at a price.

Reflector telescopes use two mirrors to focus light at the eye piece. A primary concaved mirror concentrates light and a smaller secondary mirror reflects the light out of the optical system to the eye piece as demonstrated in the animated graphic below. Because mirrors can be thicker and are easier to seat than lenses, the aperture size of reflectors can be far larger than their refracting brethren.

Telescopes For Beginners - Reflecting Telescopes


Featured Telescope - Meade ETX LS 6" ACF Telescope with LightSwitch
If you are looking for a beginners telescope to last a life time, look no further than Meades 6" LTX LS

Meade ETX LS - General Features;
  • High quality 6 inch catadioptric
  • Optical Design Advanced Coma-Free (ACF)
  • Primary Mirror Diameter 6" (152mm
  • Focal Length, Focal Ratio 1524mm, f/10
  • Ultra-High Transmission Coatings (UHTCTM)
  • Built in CCD imaging
  • Primary Mirror Material Pyrex® Glass
Meade's revolutionary ETX-LS LightSwitch telescopes use advanced technologies like GPS, LNTTM and ECLIPSTM CCD imaging to do what no other consumer telescope has done before: take all the hassle out of using a telescope.



Modern telescope designs under the Catadioptric umbrella like our featured telescope, the stunning Meade ETX LS, include Schmidt-Cassegrains and Maksutov-Cassegrains. These telescopes combine a lens and mirrors to put large apertures and long focal lengths into a compact size at a reasonable cost. Catadioptric designs incorporate an opening in the primary mirror which allows light reflected from the secondary to pass through the primary to the eye piece as demonstrated in the following graphic.

Telescopes For Beginners - Catadioptric Telescopes


The different types of telescopes described in this article are demonstrated in the following video from Watchmojo.com.




  Telescope Mounts

The mount is as important as the telescope itself, it has to provide a solid structure to hold and support the scope and a means to smoothly control its motion. An under engineered mount will kill a good instruments ability to perform. Unless you are looking to seperately marry the telescope and mount yourself, most good telescopes are packaged with appropriately engineered mounts.

There are two main mount types available commercially, Altazimuth and Equatorial. Altazimuth mounts are simpler than equatorial having two axes of motion, vertical (altitude) and horizontal (azimuth). Most altazimuth mounts will have hand operated slow motion controls for accurate adjustments in both axes and/or motorised/computerised controls.

A version of the altazimuth mount is used in Dobsonian reflector design, the main part of the mount being a heavy base with the scope mounted close to ground level eliminating the need for a potential unstable tripod. With this structurally stable advantage Dobsonian reflectors can easily support large aperture objectives.

Equatorial mounts are polar aligned and are essential if medium to long exposure astrophotography is being considered. Hand guided equatorial mounts are general considered superior to un-motorised altazimuth mounts as adjustments in only one axis is needed.

Modern Catadioptric telescopes are mainly altazimuth fork mounts controlled in both axes by an on board computer. An equatorial wedge can be added for long exposure astrophotography, in this case the unused axis is disabled.

  Advantages And Disadvantages

  • Price; Mirrors cost less to manufacture than lenses therefore reflectors will be cheaper per inch of aperture size.

  • Colour Errors; Mirrors reflect light so remain free from the colour errors associated with refracted light through lenses.

  • Alignment; The optical system will need to be aligned periodically on reflectors; this is termed collimation which is not required with refractors.

  • Maintenance; Refractors in general, are more robust, require less maintenance and cleaning as the tube assembly is sealed by the lens. Mirrors on the other hand will build up a covering of dirt overtime and may require careful cleaning.

  • Image;The secondary mirror causes light obstruction in reflectors and the mirrors holding mechanism, called a spider, causes diffraction spikes when bright objects like stars are viewed. Because the tube assembly is open, air currents and changes in air temperature can affect image stability. Refractors suffer from none of these disadvantages and the image, in general, is brighter and sharper.

Many of the disadvantages in both types of telescope have been solved with the modern Catadioptric designs. Collimation is still required and some light obstruction from the secondary mirror remains.
The following video demonstrates the initial assembly and overview of a Celestron NexStar SE Telescopes in particular, but gives a good feel for the compact Catadioptric type design in general.




  Summary

When purchasing a telescope, one of the main considerations and also limitations is budget. We will summarise then, by cost.

If you have a budget of a few hundreds of pounds to occasionally observe the moon and bright planets then a six to eight inch Dobsonian is a great beginners telescope. Easy to move and set up, you can be observing in minutes. Some knowledge of the night sky is required but then half of the fun is learning.

If you have a larger budget then an eight to ten inch Catadioptric is an excellent choice. Add an Equatorial wedge to the mount at some stage in the future and medium to long exposure astrophotography is possible. These telescopes are computer controlled and when set-up correctly will automatically slew to any one of the thousands of objects built into its database. They can also be linked to a PC reasonable easily and controlled through a number of software packages like The Sky or Starry Night.

If your budget can run to it, twelve to fourteen inch versions of the Catadioptric are amazing instruments but are large and not easy to move being better suited to a permanently located observatory. A four to six inch Apochromatic Refractor is another high budget contender and will provide stunning views of all objects.

If you still can not decide on which beginners telescope is right for you, or what you really want is currently beyond your budget, then a really great alternative while you research further or save is a good pair of binoculars. Binoculars provide beautiful wide field views of the night sky, encourage you to learn your way around it and you will be surprised how much you can see. Brighter galaxies, star clusters and rich star fields are within their grasp, they will last a life time and will still be used, even when you have purchased a telescope, for quick observing. Remember, as with telescopes, their light gathering ability is important so purchase as big as you can afford (and hold).

  Endnote

Hopefully we have made the task of choosing your beginners telescope a little easier. Choose well and your telescope will reward you with years of service and provide stunning views of the night sky.

Use the form on the Contact Us page to send corrections, alterations, additions and comments in general regarding this article, or you can post a comment on our Community pages.

Send or post your telescope reviews or experiences (good and bad) to help other first time buyers make informed decisions on the telescopes they purchase.

Thank you for reading and clear skies...

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Featured Telescope - Celestron NexStar 6 SE Computerised Telescope
If your buget allows the NexStar 6 SE is a fantasic telescope. Features of the NexStar 6 SE;
  • 6 inch/150mm Schmidt-Cassegrain telescope
  • StarBright XLT high transmission coatings
  • Ultra sturdy steel tripod with accessory tray
  • Quick release fork mount, optical tube and accessory tray
  • Proven NexStar computer control technology
  • 40,000 object database with 200 user defineable objects
  • Quick no tool set up
  • SkyAlign, Celestron's fast and easy patented alignment process
  • Flash upgradeable for downloading product updates over the internet
  • NexRemote software and RS232 cable included for advanced control via your computer