How to Buy Your First Telescope

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How to Buy Your First Telescope


As science, astronomy and physics become more popular and accessible through media such as television, demand for home technology such as telescopes has rocketed. Many people now want to get involved in this exciting new hobby, but have no idea where to start. This guide will provide the answers.

Types of Telescope

Optical telescopes are the type used by most amateur astronomers. These telescopes gather light from the visible part of the electromagnetic spectrum i.e. the area in which the human eye sees. So these telescopes are used for seeing distant objects. They differ from telescopes which see outside the visible light spectrum, such as X-Ray telescopes, UV telescopes, and Radio telescopes. Within the optical telescope range, there are three set-ups available: refractor, reflector and catadioptric. Each uses a different objective, or part of the telescope, to gather light. The telescope's sensitivity and power of magnitude is directly related to the diameter (aperture) of its primary objective. Refracting telescopes are measured in millimetres, which correspond to the size of the objective lens which gathers and focuses the light. The larger the lens, the more powerful – and more expensive – the telescope.
Reflecting telescopes are measured in inches, being the size of the primary objective mirror. As above, the larger the mirrors, the more powerful – and expensive – the telescope. As it is easier to make large mirrors than to make large lenses, most of the biggest and most powerful earth and space telescopes are reflectors.

Refracting telescope
 

Lenses
 

The lens, coupled with the eyepiece, gathers and sharpens more visible light than the human eye can, to present a magnified, clearer image to the viewer.
A 60mm diameter refracting telescope is considered a good first time buy.

 

Reflecting telescope

 

Mirrors
 

A single or combination of mirrors gathers light and projects the image through the eyepiece to the viewer. Reflecting telescopes can have very large objectives, which is why most serious space telescopes are reflecting telescopes.
A 4.5 inch reflecting telescope is considered a good first time buy.

 

Catadioptric telescope

Lenses and Mirrors
 

A combination of specially shaped mirrors and lenses to gather light and project images through the eyepiece. The combination can help to reduce aberrations caused by the bending of light which can be common in the other two types of telescope.

 


Catadioptric telescopes, because of their more complicated internal workings, are generally more expensive and more complicated. Most first time buyers should therefore look at either a reflecting or refracting telescope.

Refracting Telescopes

A refracting telescope should be easy to maintain, requiring little to no maintenance. A refracting telescope is a sealed tube and so the lens, once placed inside during manufacture, should never become misaligned unless the telescope is exposed to major trauma. By focusing the light through specially-coated lenses that prevent 'light scatter' – a common phenomenon when light is passed through glass where the red and blue colours separate out and blur the image – refracting telescopes can generate a clearer, more stable image. One disadvantage to refracting telescopes is cool down time. When taking a telescope outside to star gaze, the telescope should be mounted and left to cool to ambient temperatures. The closed-tube assembly of a refracting telescope can make this cool down a significant period of time but, once the telescope is at ambient temperature, images seen through it are clearer and more detailed. Cool down time should be factored in to any star-gazing and the telescope moved into place in good time. This is especially important if astronomers are looking for transient objects such as meteor showers or planets which only appear on the horizon for a few hours.

Reflecting Telescopes

Reflecting telescopes use mirrors coated with aluminium to reflect the most amount of light possible into the eyepiece. The use of mirrors means they do not suffer from chromatic aberration – light scatter. The primary, curved mirror collects light and bends it down to a secondary mirror, which bounces it into the eyepiece. Primary mirrors can be very large indeed and the bigger they are, the more powerful is the telescope. The secondary mirror, which reflects light into the eyepiece, causes what is known as a central obstruction. It creates some loss of contrast in the final image.
To combat this, some manufacturers have created secondary mirrors which are smaller than average. However, this can create a 'coma' effect on stars near the edge of the field of view. This means these stars look like comets, with trailing tails. Coma correctors come with some telescopes and this helps to widen the useable field of view significantly. Reflecting telescopes are quite sensitive to trauma and the mirrors can become misaligned. Great care should be taken if the telescope is put into storage or is permanently set up that it is not knocked or dropped. As with refracting telescopes, reflectors should be cooled prior to use for the clearest, most defined images to be visible.

Magnification

Many telescopes on the market make extravagant claims to their magnifying capabilities. Magnification is directly related to the diameter (or aperture) of the primary objective – the larger the lens or mirror, the further and sharper star-gazers can see. This is because light-gathering and resolution are both increased in proportion to the size of the objective.The best telescopes on the market are limited to around 50x or 75x magnification per inch of aperture. A telescope that is marketed as being able to reach 650x magnification may be technically correct, but what is visible through the eyepiece will be a complete blur. Amateurs are much better off buying a lower magnification telescope, which will give bright, clear images, albeit they will appear quite small. When purchasing a telescope, aperture is the most important consideration. Buyers should always strive to attain the largest size aperture within their budget and not opt for the largest magnification or power.

Telescope Mounts and Accessories

A sturdy, robust telescope mount is an absolute necessity for star-gazing. If a telescope is mounted on a shaky tripod, the images presented through the eyepiece will be constantly wobbling, and the telescope itself may move out of alignment with the object being viewed. The two most popular types of mount are the Alt-azimuth mount and the Equatorial mounts. An Alt-azimuth mount is one which can move – either by hand or with a motor – left and right, and up and down. This means that the telescope can be swivelled to track moving objects across the night sky or to pan from one object to another. This can help astronomers to orient themselves in the night sky. An Equatorial mount is one which counters the Earth's spin by aligning itself to the Earth's axis and moving in concert. This means it turns counter to the planet so that objects remain firmly visible through the eyepiece, rather than tracking across the sky as celestial objects seem from our vantage point to do. Other accessories for the amateur astronomer include planispheres, which are two-dimensional star maps and allow an astronomer to know where to look at any given time of year, eyepieces which can be swapped to change magnification, and filters to enable the eye to see clearer images. In this regard, exceptional care should be taken when using the sun filter and, ideally, astronomers should never look at the sun through a telescope unless they are professionals or using a professional's equipment.

How to Buy a Telescope on eBay


Most of the essential equipment required for starting out in astronomy, including the purchase of your first telescope, is available on eBay. Head to the homepage and then select Cameras & Photography from the All Categories drop down list, then on the left hand side of the page select Telescopes & Binoculars from the list and then filter the search by Telescopes, or by Telescope Parts & Accessories as necessary. Or simply type in a more specific search into the top search bar. Any matches will then be displayed.

Conclusion


Amateurs buying their first telescope should be aware that the images produced in Astronomy magazines and on the Internet are generally composites of several images taken in various light conditions and with a variety of telescopes and filters. These images are built up of several others. What an amateur will be able to see through a new telescope will not be as detailed as those professional images. However, the moon and nearby planets – Venus, Jupiter, Saturn – and their satellites, as well as constellations and nebulae, are all well within the grasp of a small telescope, and seeing them in person, in real time, can be a very special experience.

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