Beginners

LuntSolarTypes of Telescopes

Details

You’ve unpacked your telescope from its box and carefully assembled it according to the directions on the instruction booklet. “What instruction book?” I hear some of you say. If your telescope doesn’t have an instruction book, contact the place you bought the instrument from to let them know and they may be able to chase one up for you.

Regardless of the type of telescope you have bought, reflector, refractor, maksutov cassegrain or schmidt cassegrain, before using it, ensure that it is assembled properly and that the mount is stable- a wobbly telescope mount will detract from your viewing. This could be as simple as chocking up one of the legs with a piece of wood. It is a good idea to ensure that the tripod is level even for an alt-azimuth mount, and essential for an equatorial arrangement.

If you have a finderscope or finder attached to the side of the main tube, it’s important that it is correctly aligned. You use this to aim the main telescope and find the objects you are looking for. This is a necessary piece of equipment as it is extremely difficult to locate objects even bright ones like the moon through the main tube. The best time to align your finder is during the day. To do this, locate a distant terrestrial object, like the top of a telegraph pole or a tall tree, through the main scope and centre the object as close as possible. Then adjust the screws on the finder to move it so that the object in your main scope is centered in the cross hairs of your finder. Carefully tighten the screws keeping the object centered in the crosshairs. Your finder is now aligned.

BE VERY CAREFUL THAT YOU DO NOT AIM YOUR FINDER OR TELESCOPE AT THE SUN!

Once you are ready to start observing, start off with a low magnification eyepiece such as a 25mm, or even a 40mm if your telescope has a long focal length. It will be much easier to center the object in your telescope. This applies to bright objects such as the moon or planets as well as fainter objects such as clusters. Check the alignment of your finder with your main tube again on a relatively bright star. Adjust if necessary but remember that the stars are moving. It is important to do this to ensure easier location of objects.

If the objects in your eyepiece appear to be unsteady, it can be because the atmospheric conditions are unstable (usually caused by moisture in the air, wind or heat). Astronomers call this “bad seeing” and no amount of magnification will help you. Higher magnification just magnifies the bad conditions. You are better off using low power or even packing up. All nights are not the same and conditions can and will change as the night progresses. A good way of checking for seeing is to look at the sky and seeing if all the stars are twinkling, not just the ones lower down in the sky. Our atmosphere causes the twinkling effect and if the stars overhead are not twinkling too much, the seeing will probably be quite good. Make sure you set up your telescope on grass and not a solid surface such as concrete or asphalt, as they tend to retain the heat built up during the day. As hot air rises, this can also cause heat distortion in your telescope. It is a good idea to leave your telescope set up outside for a while before you start viewing, as it takes time for your mirror or lenses to cool down. The cooler the mirror or lens, the better the image you get.

The best way of learning to use your telescope effectively is to join an astronomical club. No matter what size telescope you have, if you don’t use it properly, it is a waste of money. We at SEQAS offer a service to the public where you can learn to do this at no charge. (See the Urban Observers Group) We cater for all whether you are a beginner or have more experience.

Now a word on magnification. The most important thing to remember when purchasing a telescope is aperture or how wide the telescope is. The bigger the aperture, the bigger and brighter the image. So get the largest telescope you can afford. You won’t be sorry. A lot of telescopes are sold on their magnifying power, for example ” magnifies 400x”. You think “Wow, that sounds impressive!” What exactly does this mean? Forget about seeing all those lovely images you see in magazines, books or on the boxes of telescopes. For a start, you won’t see things in colour. This is only achieved with time exposure photography. Objects such as galaxies are usually only seen as very small and faint smudges anyway in most amateur instruments.

Magnification of objects is achieved by using different powered eyepieces. Most telescopes come with at least one eyepiece. It is a good idea to invest a little more money on purchasing decent quality eyepieces. We recommend at least three- one low power eg. 25-40mm, one medium powered eg. 12-18mm and one high powered 10 and below. If you own a telescope smaller than an 8-inch (200mm) aperture, the rule of not exceeding 60x per inch of aperture is suggested. This means that an 8-inch telescope can operate theoretically at a maximum of 480x magnification, but of course this depends entirely on the seeing conditions. To work out your magnification, you divide the focal length of your telescope (how long the tube is and this information should be on your telescope somewhere or in your instruction manual) by the focal length of your eyepiece in millimetres e.g. 1250mm (length of telescope) divided by 25 mm (size of eyepiece)= 50x magnification.

Telescope Aperture versus Maximum Magnification Table.

Telescope Aperture Magnification
(in.) (cm) Theoretical Practical
2.4 6 144 100
3.1 8 186 125
4 10 255 170
6 15 360 240
8 20 480 300
10 25 600 300
12.5 32 750 300
14 36 840 300
16 41 960 300
18 46 1080 300
20 55 1200 300
25 64 1500 300
30 76 1800 300

Some handy accessories for you and your telescope are:

  • a red torch (a torch covered with red cellophane or red nail polish)
  • a compass
  • a planisphere (to help recognize the constellations)
  • some good quality books with maps or star charts
  • a case to carry all your accessories (aluminium tool cases are ideal)
  • insect repellent
  • warm clothing
  • warm footwear
  • a hat or beanie

Recommended Reading:

Magazines (available from newsagents)

  • Sky and Space
  • Astronomy
  • Australian Sky and Telescope

Books

  • Astronomy 2014 (available from our club, bookstores, Australian Geographic stores)
  • Star Ware (2nd Edition) by Philip S. Harrington
  • Sky Watching by David H. Levy
  • Advanced Sky Watching by Robert Burnham et al.
  • The Southern Sky Guide by David Ellyard and Will Tirion
  • The Southern Sky by David Reidy and Ken Wallace
  • A Walk Through the Southern Sky by Milton D. Heifetz and Will Tirion

These are by no means the only books to read on the subject. Be aware that many books are written for the Northern Hemisphere and if using any star charts from these books, they have to be turned upside down for our southern skies. They also tend to rave about the wonders they can see eg. the Andromeda Galaxy and they either gloss over things that we can see or even leave them out as not being important. The council libraries are a good source of astronomical reading material. The SEQAS library has a good selection of books available for club members to borrow. SEQAS also has telescopes for hire at reasonable rates to members.

Happy Star Gazing!

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