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Shopping for that first telescope

The first thing you need to know when buying a telescope is that telescopes do not have power.

The first question most people ask me when I'm out with my telescope is "what power is it"? The answer is "telescopes do not have power". How many times your telescope magnifies depends on your eyepiece and Barlow lens (if you use one). But there is a limit. I have an eyepiece and two Barlow lens that would allow me to magnify 3,000 times, but I would not see anything. Why? Because it is far beyond the limits of my telescope. What sets the limit? The size of the main lens or mirror. This is known as aperture. The larger the aperture the more light the telescope will gather. The more light the telescope gathers the more you can magnify and still get a clear picture. The reason I bring this up is many of the low quality telescope manufactures advertise their telescopes as having a power of 400x, 500x or even 600x or more. These telescopes are a waste of money.

This brings us to the second thing you need to know. The more aperture the better the telescope.

The reason you want more aperture is not for magnification, but for a clearer picture and to see fainter objects. You will use the most power when viewing the planets and moon. When viewing stars, galaxies and nebula, you will find that the best results require a lot less magnification. But remember, if you are buying a scope that you will be carrying in and out, more aperture is great but it has to be something you can handle.

Your best bet is to buy a good brand name.

There are many good brands with affordable prices. Meade, Celestron, and Orion are probably three of the most popular names. They also sale a wide variety of scopes which brings up the next step and maybe the most difficult decision. Picking the telescope that is most suitable for you.

The best telescope for you.

The three main types of telescopes are reflector, refractor and catadioptric (called cat for short).


The diagram above shows how a reflector telescope works. The main mirror is at the bottom of the tube. light comes in and is reflected off the main mirror to the secondary mirror which reflects it 90 degrees out the side of the telescope to the eyepiece. One advantage to this scope in our area is it's resistance to the heavy dew problem. Because the main mirror is at the bottom of the tube it does not get covered with dew easily. This type telescope is also called a Newtonian. Named after its inventor, Isaac Newton.


This diagram is a refractor telescope. The light comes in through the main lens and goes to the eyepiece at the back of the telescope. This is basically the same type telescope used by Galileo, a tube with a lens at each end. When you think of a telescope, this is probably the type you picture. If you go to my setup, the small scope I have mounted to the top of the large one is a refractor. The word refract means to redirect light without breaking it up into the colors of the spectrum. There are two types of refractors, Achromatic and Apochromatic. The Achromatics have a slight problem with false colors. A later version of the refractor, the Apochromatic, uses a three lens system to eliminate this problem. The only trouble with this is it multiplies the price by about ten. The dew problem with these scopes is not too bad because of the smaller apertures and the large dew shields.


This diagram is the cat telescope. The light comes in through the corrector lens, reflects off the main mirror in the back which reflects it back to the secondary mirror in the front. The secondary mirror reflects it through an opening in the back to the eyepiece. The one in the diagram is a Schmidt-Cassegrain, the same as my main scope. The corrector lens was invented by a man named Schmidt and the mirror system by a man named Cassegrain. There is a big dew problem with this scope because of the large lens up front. I have a dew shield for mine but it doesn't help much. The best weapon on the war against dew is a hair dryer.

The telescope in the picture to the left is called a Dobsonian. It was invented by John Dobson in order to bring larger aperture telescopes to amateur astronomers. I have never owned a Dobsonian, but Terence Dickinson and Alan Dyer in their book "The Backyard Astronomer's Guide" say these are great starter scopes because they are easy to set up, easy to operate and you can get more aperture for the dollar. One of the problems with this scope is its appearance. It looks more like a cannon than the traditional telescope and to some this may be a problem, especially the younger astronomers.


This is my small reflector telescope on an equatorial mount.
		This is a Criterion Dynamax 8 that was made in the 70's. It's a Schmidt-Cassegrain on an equatorial mount called a wedge.

	This is two refractor telescopes. The closest one is on an altazimuth mount. The white telescope in the back is on an equatorial mount.

The next thing you need to decide is the type of mount.

In the pictures above you see the two types of mounts; equatorial and altazimuth. The equatorial mount can be of the axis or the wedge type. The advantage of the equatorial mount is when you have the axis, or in the case of the wedge, the forks of the telescope, pointed at the celestial north, while tracking an object you only have to move the telescope in the east and west direction.

Another type of mount is called the "Go To". These are computer controlled mounts that automatically slew to a chosen object with the push of a button. There are two disadvantages with the "Go To" scopes. The first one is they can be very expensive. The next is they tend to make you lazy. I think it's important to learn your way around the sky using constellations, stars and star charts, but with a "Go To" scope you tend not to study as hard. One of the most exciting moments for a beginner is using a sky chart to pinpoint a deep sky object, then find it with a telescope.

Where do you buy a telescope?

The best store in our area for telescopes is "Wonder Works". They keep a few smaller ones in stock and if you can't find what you want, they can order you one. They also have a good selection of accessories. Some of the camera stores in the area also carry a limited supply. The next choice would be the internet. I have shopped at many internet sites but my two favorite ones are buytelescopes.com and telescopes.com. I have also found some great deals on ebay.

I hope this helps you in your search for a telescope. If you have a question you would like to ask me please contact me.