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Frequently Asked Questions 

How to Use a Telescope

QUESTION: My wife and I are looking for some help learning to use our telescope. Neither one of us has any experience using one. Any help would be greatly appreciated.

ANSWER: The first thing you will need to know is does your telescope have a polar axis or not, that is, is it intended to track, or is it merely a point and look, or what we call Alt-Az. Alt means altitude and Az means azimuth, where Alt is the distance above the horizon, and Az is the direction in a circle around the horizon. If you have an Alt-Az mount, just skip the polar alignment step.

If you have a polar axis, that is, your telescope is intended to track the stars, then find north, and make sure the polar axis is approximately lined up in that direction. It does not have to be too accurate, but make sure it is pointing pretty close to north. If you are not sure where north is, either use a magnetic compass, or try to find Polaris, the North Star. 

For instructions on precise polar alignment, see our FAQ on How to Align an Astronomical Telescope.

Now your are ready to align the finder scope. 

You will have to find a way to align your finderscope so that it is in line and points to the same thing you see in the eyepiece. Then you can use it to find objects of interest. The best way to do this is to find the lowest power eyepiece you have, and use it to find a bright planet like Juipter, or even the moon. Once you get Jupiter centered in the eyepiece of your telescope, and if your telescope tracks, lock down the drive to follow the planet so it will stay centered in the eyepiece. If your telescope does not track, then just re-center the planet in the eyepiece from time to time.

Now, look at the finder scope. I assume it is a scope. It should have somewhere on the mount at least one set of three thumb screws holding the finderscope in place. Gently loosen the screws on the finderscope and look through its eyepiece. You should see a cross hair or "X". Align the planet on the cross hair by alternately adjusting the screws until it stays centered. When it is, try to tighten the screws so it holds the finderscope securely. Now your finderscope is aligned with the telescope eyepiece, and you should be able to use it to find other objects of interest.

If aligning the finderscope is too hard to do at night, then try doing the alignment during the day, by finding the top of a telephone pole, a radio tower, or similar object, at least a mile distant, and use it for aligning the finder scope. Then wait for nightfall.

Be aware that finderscopes loose their alignment quite easily, because those screws can be rattled loose, so you will have to do this often. Be sure to check the alignment every time you use the telescope, and realign if necessary.

You are now ready to use your telescope.


Viewing Things Right-Side Up

QUESTION: Help! I know nothing about telescopes and a friend gave my 8 yr old son one. Why are things upside down? Is this normal?

ANSWER: Things always look upside down in an astronomical telescope. This is perfectly normal, and there is nothing wrong with your instrument.

Things look right-side up  in a pair of binoculars because they have a prism that flips the image for normal viewing.

If you want to use your telescope to view terrestrial objects during the day, you will need to get an erecting prism. Try contacting Orion Telescopes in California, http://www.oriontel.com/.

If you are using your telescope to view astronomical objects at night, this is not nearly as much of a problem. In fact, most astronomers quickly get used to the inverted views in their telescopes.

Please keep in mind that this is a perfectly normal characteristic of astronomical telescopes, and that there is nothing wrong with your equipment.


 Why Do I See Dark?

QUESTION: When I look in the eyepiece all I see is dark. I am using the lowest power lens tonight because it is not especially bright. I have also changed to the higher power but with the same result. We have a 6mm and a 20mm lens, as well as an adapter that changes the magnification of each by approx. 3x.

ANSWER: Make sure that there is no lens cover at the front of the telescope, and no obstructions inside the tube or on the eyepiece. Sometimes the eyepieces may have a dust-cap, so look carefully. If you have any doubt, try looking at things with the telescope during the day to make sure things are OK.

My advice is, forget about the 6mm eyepiece and use only the 20mm, especially for finding things. Use the 6mm only for viewing planets and the moon after you have found them using the 20mm. The higher power eyepiece is designed for seeing detail after your have found the object you are looking for. 

The attachment that magnifies things by 3x is called a Barlow lens. Use the Barlow only after you find a planet and lock onto it. Most amateur astronomers hardly ever use the higher power eyepieces, except when looking for lunar or planetary detail. In fact, you may never even want to use the Barlow.

Good Luck.


Using a Barlow Lens

QUESTION: Hi. My son and I just signed up for the Astronomical League and are looking forward to joining. In the meantime, we have a question that maybe you can help us with. We recently purchased a Meade 90ETC and just got a Barlow lens (total magnification is 96X), and when we look at the stars now we see a donut shape, light around a black center. Is this a result of the optics of the lens or a result of the diffraction of light from the star? Any insight you can provide will be greatly appreciated.

ANSWER: Congratulations on your purchase of a Meade ETX telescope. This is a very popular telescope and is an excellent choice for beginners. You should have many years of use from it.

You asked about the donut shaped star images seen in your eyepiece when you use the Barlow lens. This is caused by the configuration of the optical system used in the telescope. If you look at the front (corrector plate) of the telescope, you will see a round circle about an inch wide or so. This is the secondary mirror which reflects light back from the primary mirror to the eyepiece in the back. When your eyepiece is out of focus, you will be able to see the outline of this secondary. It should go away when you focus the image sharply in the eyepiece. This is not a defect unless you cannot get the scope to focus at all.

You might take into consideration that if either one of the observers wears glasses, and focuses for his own vision, it is likely that the other observer will have to refocus. For this reason, if you wear glasses, and intend someone else to look at what you have focused on, it is a good idea to wear your glasses while focusing, so the image will be clear for your friend.

I hope this helps a bit. There is a lot to say about this subject, but I think I have answered your question.

There is a web page on the internet devoted to the ETX. It is Mike Weasner's Mighty ETX site. The URL is http://www.weasner.com/etx/

Ed Flaspoehler, President
American Association of Amateur Astronomers
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