Telescope Guide

BUYING THE RIGHT TELESCOPE

There are two types of "telescope" - the SPOTTING SCOPE which is suitable for daytime viewing of land-based objects, and the ASTRONOMICAL TELESCOPE which is suitable for observation of the night sky.

SPOTTING SCOPES (TERRESTRIAL VIEWING)

SPOTTING SCOPES are designed for viewing land objects and produces erected or "right side up" images. They are monoculars (half a binocular) with a much higher magnification and objective diameter than binoculars making them suitable for bird-watching, wildlife viewing, and star-gazing. Unlike monoculars, but like telescopes, spotting-scopes require mounting on a tripod because the high magnification produces unstable images when hand-held.

They normally come with one zoom eyepiece - most often 15-36x or 20-60x magnification. Spotting scopes with a bigger objective lens (the one at the front) give brighter images but make the scope bigger and more expensive.
Some come with an adapter so that you can mount on your SLR camera and use as a powerful telephoto lens. Others are waterproof so you don't have to worry about the weather.

You can use a refracting astronomical telescope for terrestrial viewing but the images will either be upside down or flipped from right to left. The image can be viewed correctly with the addition of an erecting eyepiece (sometimes included with telescope but often an optional extra).

ASTRONOMICAL TELESCOPES (ASTRONOMICAL VIEWING)
Naked eye observation of the stars is limited by the lens-diameter of the human eye. The Astronomical telescope, serving as a much larger "eye", collects more light and permits the observation of objects in tremendously increased detail.  Because they offer high magnification they must be mounted on the tripod supplied with the telescope

BUYING THE RIGHT ASTRONOMICAL TELESCOPE
Only you can choose the type of telescope best suited to your particular purpose, usage conditions, and budget considerations. However, be careful when choosing a telescope. Some cheap telescopes (in particular 60mm refractors) are nearly impossible to focus and produce dim, fuzzy images that quickly discourage the beginning astronomer. Also, many of these units have flimsy tripods that will fall over at the slightest touch. In general, telescopes with plastic tubes and/or plastic objective lenses are not built to last and will not give high quality images. If you are serious about astronomy your telescope should be all metal with glass (preferably precision optical glass) accessories.

UNDERSTANDING THOSE NUMBERS and WORDS

The most important operative characteristic of an astronomical telescope is its aperture, or diameter, not magnification as is often thought. The larger the aperture the brighter and better-resolved the image becomes (e.g. an 80 mm aperture collects 131 times the amount of light collected by the naked eye).

The magnifying power at which a telescope is operating is determined by the eyepiece employed: changing the eyepiece causes a change in the operating power. To calculate power, divide the focal length of the eyepiece into the focal length of the telescope. The higher the magnification the closer the object being viewed appears to be in the viewfinder. A finderscope is an accessory with a very low magnification to allow location of the object being viewed.

An altazimuth (altitude-azimuth) mount has two axes of rotation, a horizontal axis and a vertical axis. To point the telescope at an object, you rotate it along the horizon (azimuth axis) to the object's horizontal position, and then tilt the telescope, along the altitude axis, to the object's vertical position. This type of mount is simple to use, and is most common in inexpensive telescopes.

The more sophisticated equatorial mount also has two perpendicular axes of rotation - right ascension and declination. However, instead of being oriented up and down, it is tilted at the same angle as the Earth's axis of rotation. When properly aligned with the Earth's poles, equatorial mounts can allow the telescope to follow the smooth, arc-like motion of a star across the sky. You need an equatorial mount for astro-photography.

Beginner Astronomer

The 60mm refractor is the most popular telescope size for the beginning astronomer, the terrestrial observer, or for casual gift giving. It can introduce newcomers to the exciting hobby of astronomy at an affordable price or be used to observe wildlife and take in distant views.
With a good quality 60mm refractor all of the following objects can be observed sharply and clearly:

- Saturn's magnificent ring system and its largest moon
- Jupiter's distinctive cloud belt and four principal satellites
- Venus and it's moon-like phases
- the Moon and its craters, mountain ranges and rills
- a multitude of deep-space objects including nebulae, galaxies, and star clusters
- high-resolution views of terrestrial objects such as reading a license plate that is more than a kilometre away or resolving the feather structure of a bird at 50m (as mentioned above, these may not be oriented correctly but this can be corrected with an erecting eyepiece).

The Intermediate Amateur Astronomer

The intermediate amateur astronomer will want increased image brightness and resolution and to be able to track astronomical objects as they move across the sky.
Refracting telescopes with 90 mm apertures and sophisticated equatorial mounts are recommended. A 90mm refractor will provide 125% brighter images than a 60mm refractor.

For astronomy you can enjoy breathtaking views of the Moon, Saturn with its ring structure, Jupiter and its belts, and hundreds of deep-space objects including galaxies, nebulae, and star clusters.
For terrestrial use, enjoy views from afar or take your instrument out in the field to take advantage of our natural environment up close.

The Serious Amateur Astronomer

The 115mm (4.5") Reflecting telescopes (with 3.7 times the light collection area of 60mm refractors) are especially advantageous for deep-space observation of galaxies and nebulae. The addition of an electric motor drive system which automatically tracks astronomical objects across the sky would also be appreciated by a very serious astronomer.

These larger aperture telescopes allow the divisions in Saturn's rings to become visible: Jupiter's belt structure takes on added character and land objects are better resolved. It should be noted that refracting telescopes are more suitable than reflecting for land-viewing because of their convenient image orientation and location.

Advanced Astronomy

If your interest in the moon, planets, and deep-space becomes serious and sustained you will probably want to invest more money and move up to an 8" or 10" mirror lens telescope. These have 11 times and 17 times the light collection area of a 60mm refractor respectively and permit the observation of delicate structures such as :

- dust lanes in external galaxies
- the examination of extremely well resolved lunar and planetary detail
- the study of thousands of celestial objects

SUMMARY OF TELESCOPE TYPES AND USES

TELESCOPE EYEPIECES

Most telescopes only come with one or two eyepieces so your first purchase may be additional eyepieces. Eye piece quality is very important.  Good eye pieces cost upwards of $130 so avoid cheap ones which usually only have plastic lenses. The lowest priced, quality eyepieces are the Achromatic eyepieces  and more expensive, but better quality, are the "Plossl" eyepieces.

A very effective way to get higher magnifications is with a Barlow Lens. This is a "teleconverter" eyepiece that doubles, or triples,  the power of any standard eyepiece.  They are especially good with medium focal length eyepieces (20mm to 10mm focal length) and with Reflector Telescopes. Every serious owner should have a Barlow.
 

TELESCOPE PHOTOGRAPHY

It is possible to capture photographs through a spotting scope or a telescope. As only some models have this capability you must know beforehand that you intend to take photos so you don't buy a model without the capability. You will also need to purchase a T-mount to fit your SLR body and a camera adapter to fit the T-mount to the telescope. The telescope then become a telephoto lens for the camera. 

Because Earth is rotating the celestial objects will move across your field of view as you look at them for a few minutes or longer. Consequently the slow shutter speeds required to obtain an image from a "dark sky" will record this movement and you will get  streaks rather than dots. The only way to overcome this is to use a very high ISO or add an electric motor drive system to your telescope

COMPUTER AIDED TELESCOPES

To simplify your star-gazing there are now computer-aided versions of the above telescopes that locate celestial objects without calculations or astronomical knowledge.  

The Tasco Starguide series of telescopes are one range of computer-aided telescopes. Computerized hand-controls and an auto-align feature automatically locate more than 1,800 pre-programmed celestial objects. The advanced StarPointer™ pinpoints locations, while electronic slow motion controls provide fine-tuning for extended viewing. Currently there are three model in the Tasco Starguide range - a 60mm & 80mm refractor and 114mm reflector. Contact us for more details