25Jul2017

Guide To Buying Your First Telescope

Related image

One great thing about astronomy is that you don’t need any fancy or expensive equipment to get started. A warm coat, clear skies and a sense of intrigue about what’s up there are all that is needed.

You are now ready  to begin your adventure in this wonderful hobby. But there comes a time, naturally, when your thoughts turn to delving deeper into the heavens and when that happens most people start to think about getting a telescope.

If you’re at that point now, this article will guide you through the process of selecting your first telescope, from the factors to look for in an instrument, the different types as well as essential parts like the aperture and mount.

Image result for using telescopesWhich factors should you keep in mind when selecting a telescope?
First, the magnification, which is the number of times greater in size an object appears when viewed through a telescope. Stay away from telescopes that are publicized by their amplification — particularly unrealistically high powers like 600×.

Why? There is no theoretical limit on power, but there’s a practical limit beyond which the images obtained are worthless. Because of the way light behaves, the maximum usable magnification is about 50 times the aperture in inches. Using magnifications much beyond this will make the picture dim and very fuzzy, like using a microscope on a newspaper picture or blowing up a photograph too much.

A scope with a low magnification will do just great. Astronomical objects aren’t necessarily small, they’re just far away. Thus, light collection is of more importance than the power of the telescope. This brings us to this old saying, “Aperture wins”. A larger practical sized telescope will always show more compared to a smaller one.

Unfortunately, as the collection area becomes larger, the scope’s weight increases. As such, you need a larger mount to support it. This will keep the optics pointed to where they should be and in case it’s shaky the entire experience becomes very unpleasant.

 
Choosing the right telescope type

Refractors.
When picturing a telescope, chances are you’re thinking of the refracting telescope. Invented in the 1600’s in the Netherlands and propelled to fame by Galileo Galilei, this telescope utilizes a carefully made system of lenses that relies on the refraction of light to give beautiful images of the sky.

Most refracting telescopes utilize two lenses: an objective lens in front and a smaller eyepiece lens. Usually, the eyepiece goes into an eyepiece diagonal (an accessory which turns the light through 90 degrees) to permit comfortable viewing.

Refractors are particularly good if you wish to view the planets, double-stars or the moon (Though they are used for any subject with experience). They show great detail for their size and when used on the relatively bright planets, the objects are easy to locate, even given the small field of view.

One limitation common especially to lower priced refracting telescopes is chromatic aberration. Simply, this is the color blurring and fringing of objects. It happens because the different light frequencies do not all refract the same; think of sun light being refracted through a prism to produce a rainbow effect. The same thing happens when refracting light through telescope lenses.

This is more pronounced on bright objects such as the planets and the moon, but not noticeable with dim stars. Higher prices in this category, are primarily attributable to bigger apertures and better optics for reducing the Chromatic Aberration.

Advantages.
• Their simpler design means that these telescopes are easy to use, low maintenance and highly transportable.

• They are excellent for binary, lunar and planetary stargazing especially with larger apertures.

• Sealed tube protects the optics and prevents image degrading.

Disadvantages.
• Generally these telescopes have small apertures, typically 3 to 5 inches.

• Smaller apertures mean poor views of distant galaxies and nebulae.

• Heavier, bulkier and longer than reflector and compound telescopes of similar aperture.

• Good quality refractors cost much more for every inch of aperture as compared to other telescope types.

Reflector.
Instead of using lenses to gather light, a Newtonian reflector uses a curved, metal mirror (primary mirror) placed at the lower end of a tube to collect and reflect light to a focus. Light first enters through the telescope top. The primary mirror reflects the light back upwards to a secondary mirror placed higher up.

Image result for using telescopesThis mirror deflects the light beam by 90 degrees, thereby directing it into a focuser, and finally into an eyepiece. Focusing takes place by turning a focus wheel on the focuser so that the eyepiece is moved towards or away from the telescope tube.

Reflector telescopes tend to be short, but with a larger diameter. They’re therefore much more compact if space is an issue. But, they are much more delicate and if transporting from site to site, they will need “collimating” (essentially, calibrating the mirrors) before each use. Their larger aperture makes these telescopes brighter, and therefore better for viewing very distant or dimmer celestial objects.

These telescopes are relatively cheap for the size of mirror you’ll get for your money – ideal if you’re just starting out. A Newtonian reflector with a 6-inch (150mm) mirror will give you good views of the brighter galaxies and nebulae, and should also perform well when you train it on the planets and moon.

Advantages.
• Cheapest design (especially on Dobsonian mounts).

• More portable compared to refractor telescopes of similar aperture.

• Inherently color-free (no chromatic aberration).

Disadvantages.
• Secondary obstruction leads to loss of contrast.

• Still large compared with Schmidt Cassegrain.

• Requires frequent collimation.
Compound/ Catadioptric telescope.
Compact telescopes combine both designs to create a solid middle choice. They are generally somewhere between the refractor and reflector in price and quality.

Image result for using telescopes celestronThe telescope features 2 mirrors (one at the back and the other infront) plus a lens. Light passes through the correcting lens before being bounced off the curved primary mirror, to a secondary mirror, and finally to the eyepiece. This essentially “folds” the optics, producing incredibly detailed images within a small space. The enclosed tube lessens the amount of dust getting inside, but it needs to be cleaned occasionally.

There are 2 types of compound telescopes: Schmidt Cassegrain and Maksutov Cassegrain. The Maksutov uses a smaller mirror and thicker lens than the Schmidt. Though this makes it slightly heavier, the Maksutov produces slightly sharper images.

Advantages.
• Great for taking views of faint objects.

• Works great for objects on earth.

• Sealed tube to protect the optics.

• Great for astrophotography.

Disadvantages.
• Usually more expensive.

• Large, bulky appearance.

• Second mirror reduces brightness.

Aperture.
The most important thing in your telescope’s ability to detect anything is its aperture–diameter of the primary mirror (reflector) or objective lens (refractor). The aperture’s diameter (D) will be expressed either in millimeters or, less commonly, in inches (1 inch equals 25.4 mm).

Related image

The aperture tells you how sharp (resolving power) and bright( light-gathering ability) an object will be. A telescope’s function is to simply enhance the light of stars, galaxies and the moon thus allowing us to see them in the dark.

Having a scope with a large aperture is like having bigger eyes to view the sky. The maximum pupil diameter in humans is only 7 millimeters at full dilation. All the light the retina receives is what squeezes in through our tiny pupils. No wonder we can only discern bright deep-space objects!

Man made scopes provide the remedy for this. A telescope with just a 6” aperture will gather more than 500 times more light than human eyes can gather on their own. Its optics then focuses this light to a beam that can get through the pupil. Voila! We are able to see even dimmer objects. This is why aperture is so important.

NOTE: Although a large aperture results in a brighter and better image it will also mean that your scope will be larger and heavier. When choosing the best aperture for your needs, take time to think about where you intend to use your scope.

Effective astronomy requires viewing from a dark location which is not always available in urban areas. If you need to travel to use your scope then you need to consider how portable it is and consider choosing a telescope that has a lower aperture but is easier to setup and move around.

In a refractor telescope, look for a minimum diameter of 60 mm, but 80 mm will see more. This offers nice views of the brighter planets, the Moon, double stars, and brighter nebulae and clusters.
In a reflector, diameters of 6 or 8 inches are common and affordable. They will outperform the refractor telescope by showing dimmer nebulae, galaxies and clusters, especially from a dark sky, while still showing the same brighter objects.

Mount of the telescope.
The mount is as important as the scope. Without a solid, steady mounting, you can’t even focus properly. The heavier the mount is the better it will be, because it will be a solid platform for the telescope to rest on.

However, its weight must be offset by just how portable you need your scope to be. It shouldn’t have flimsy parts and it should never flex or wobble noticeably.

Altazimuth Telescope Mounts.
If you’re among the millions of photographers who use camera tripods, you must be the owner of atleast one altazimuth mount. It’s not the tripod legs that make a tripod an altazimuth mount, but rather the “head” sitting on top and the way it moves. Altazimuths are some of the most common mounts used to support cameras, spotting scopes, and telescopes.

Image result for telescope mountAltazimuth mounts allow users to move the scope in straight lines – right, left, up and down. The name is based on the altitude motion (up/down) and the azimuth motion (side-to-side).

Modern scopes with Altazimuths often have a manual, slow motion adjustment knob or computer control to track objects. If you are a beginner, computerized control will locate many more objects in a single night than you could find on your own. You do not have to be highly technical, since most telescope computers are user-friendly and relatively simple to operate.

Computerized control is highly recommended when observing under poorly lit skies. Navigating by your own with a star map is tough when you can’t see a lot of stars. However, computers significantly add to the price of an optical telescope. If on a budget, note that you will not be able to buy as large of a telescope if you opt for a computer.

Equatorial Telescope Mounts.
Every telescope mount has two axes upon which it independently turns, to allow the scope to point at any spot in the sky. Equatorial mounts are special in that one of their rotation axes is aligned with the axis of the Earth. This makes tracking easier. If you align one axis of an equatorial mount on Polaris, you can track celestial targets as the Earth spins by moving the scope around just this one axis.

Many equatorial telescope mounts have a motor to do this for you. Motor tracking is especially useful for high-magnification viewing and for showing celestial objects to groups of people. It’s also a prerequisite for most through-the-telescope photography.

Dobsonian Telescope Mounts.
These are variants of the Altazimuth mounts but with the base actually standing on the ground. The telescope has friction plates that are used to control elevation. This telescope offers a large aperture for a relatively low price.

Dobsonian mounts make the telescope easy to point at the deep-sky object or planet of your choice. They are strong and sturdy so you can offer views through the eyepiece to family and friends without worry of them damaging your equipment. Their manual control gives users a sense of being “lost in space”, and makes “star-hopping” under a moon less sky unforgettable.

Image result for using telescopes

Although a dob can be large, it is easily controllable by hand. However, it’s very awkward to transport around. If you’re making all your observations from the driveway or own a bigger vehicle to carry it, this won’t be a big deal, however, if you wish to pack the telescope in a modest vehicle it becomes more of an issue.

Also, the dob needs collimation. What this means is that if you wish to get good quality images, you have to align its two mirrors with each other. This is true in both high and low powers. The procedure of collimation is not hard, though it can be intimidating at first.

Telescopes are a great recreational tool as they make the heavens look bigger, brighter and closer. But perhaps a more significant contribution of telescopy to society lies in the area of science education in raising public awareness of science, conveying scientific concepts to students, and contributing to educating a technically capable and aware citizenry.

Whether you need one for recreational or educational purposes, I hope this guide will help you to make the right choice when purchasing your telescope. If you are looking for portability a Cassegrain telescope is good, and for performance a reflecting telescope would be great. If you wish to get a bang for your bucks the Dob is hard to beat, and for an all-round performer a refracting telescope is the one to look at.

Story Supplied by: Betty Miller

Read previous post:
poet
Some Space Poetry From The Pen Of Mary Branford

Maria Branford specializes  in poetry that touches the soul. Te...

moon
Scientists Spy New Evidence Of Water In The Moon’s Interior

A new study of satellite data finds that numerous volcanic...

eyes
Nasa Says Unsafe Eclipse Glasses Being Distributed

NASA issued a warning Thursday to let people know unsafe...

Close