Friday, July 27, 2007

Buying a Telescope

Bob I'm thinking of getting into Astrology, what should I be looking for in a telescope? Well first of all I explain the difference between the 2, "Astronomy not Astrology" , then if I haven't bored them to tears and they are still with me, I try to explain what to look for in a scope.

When I first decided to buy a scope I was overwhelmed at the amount of information on the internet, not only about what to look for when purchasing one but the amount of variations of telescopes that are out there. Buying a telescope can be a bit confusing, I hope to be able to make it a little easier by passing on some of the knowledge and experience I have gained through buying and selling as well as using many different types of telescopes.

Before taking the big plunge get to know the night sky, a good book to get is "The Backyard Astronomer's Guide" . If you have binoculars, use them, with them you can see dozens of lunar craters, dozens of star clusters. several nebulae and 7 planets. Get yourself a sky atlas and learn the constellations and where some of the brighter galaxies and nebulae are. An excellent sky atlas is "Sky Atlas" . Once your familiar with the night sky your ready to go.

Where to start? There are a lot of different types of telescopes out there, but they generally fall into 1 of 3 types.

  1. Refractor type; The light goes through a lense and is refracted to the eyepiece to form an image. This is the type of scope you see in all your tv programs and movies, usually in the corner of somebodies apt. since they are ideal for city apt dwellers. It is the most expensive of the 3 types per inch of aperture, ( diameter of mirror/lense of the telescope). This type of scope is excellent for viewing the planets and lunar surface. An example is the "Celestron First Scope", I have used this scope before and was very satisfied with its performance. The main disadvantage of the refractor is the high cost for the larger apertures which is what you need if you want to view deep sky items such as nebulae and galaxies.

  2. Reflector type; this type uses mirrors to gather light and form images, It is the best value for your money. an excellent telescope is Celestron 6" Starhopper . Notice The 3.5 inch refractor above costs the same as the 6" starhopper reflector. Also note the 2 different types of mounts. The refractor has an alt-az mount, simple up/down(altitude) left/right(azimuth), the Starhopper has a dobsonian mount, which is a type of alt-az mount with a low center of gravity which glides very easily just using your fingers. The dobsonian mount is used a lot on your bigger aperture amateur telescopes. I owned a Celestron 10" Starhopper for many years and highly recommend either the 6" or 10" for deep sky and planet/lunar viewing.

  3. Catadioptric/Compound type; this type of scope uses a combination of mirrors and lenses to gather and form images. A very popular type of this category of scope is the Schmidt-Cassegrain, the 8" aperture model has been the top selling serious recreational telescope. Its combination of generous aperture, portability, astrophotography adaptability and overall good performance has made it the telescope of choice for the serious Backyard astronomer. I have the Meade LX 200r and highly recommend it.

You know the 3 basic types of telescopes, now you have to make a decision on how much you want to spend and what you want to get out of the hobby. For $299.00 you can get a 3.5 inch refractor or a 6" reflector, the 6" reflector will allow you to see more deepsky objects but at the cost of portability, what is more important to you? Bigger is not neccessarily better especially if you live on the 5th. floor of an apartment, chances are on the 5th. floor of apartment there is so much light pollution that no matter how big your scope is it wouldnt be able to gather enough light to view deepsky objects, but the refractor would be portable and be perfect for lunar and planetary viewing, since light pollution does not hinder their viewing. If you are looking for a telescope primarily to view deepsky objects then you want a minimum of 6" aperture. The Celestron Starhopper above would be a good pick.

Changing magnification of your scope is as easy as changing eyepieces, which brings us to another point, what is your scopes maximum magnification? A simple rule of thumb is 50x per inch of aperture, so if you bought the 6" starhopper your maximum magnification would be 300x and thats on a good night. It may intrest you to know that the magnification I use the most is only 120x I have a 12" scope and can go up to 600x, but I rarely do, I have gone to 450x on Saturn and Mars, but on the deepsky objects it is anywhere from 40-120x.

How do you calculate magnfication? Well every scope has a focal length, the distance from the primary mirror/lense to the point at which it forms an image (eyepiece), it will be in your manual or on your scope near the eyepiece. Every eyepiece also has a focal length, a 25mm comes with the above Starhopper, The Starhopper's focal length is 48 inches or 1200mm, to determine the magnification, simply divide the focal length of the scope (1200mm) by that of the eyepiece, so the (25mm) will produce 48x. You'll notice that this is one of the few hobbies that uses both inches and mm, which confuses everything even more.

I have just lightly touched on some of the basic things to look for when considering a scope primarily for visual use. My pick would be a 6"-10" reflector on a dobsonian mount. Celestron, Meade or Orion are all very good companies to deal with. For astrophotography you get into more expensive computerized telescopes, equatorial mounts and the more expensive apo refractors which I will get into in later posts. Another guide to follow is Sky and Telescope . I'll leave you with a youtube video on what to look for when buying your first scope. Purchasing your first scope


Yours Truly said...

Ohh wow, you know a lot about telescope..

my nephew will be really interested in this.. i will hook him up to this ..

take care

yours truly,

Rocky John M. Tayaban said...

Hi there,
Hi I saw your message at Blogcatalog. Just dropping by to your blog. Interesting post you've got here. Keep up the good work.

Blogging Mix

Bob Johnson said...

yours truly, thanks! if he has any questions just email me. thanks as well rocky john m. tayaban!

Claudio said...

Wow... this is for sure the first blog I read bout astronomy... Its really interesting... I am really into this... of course not as much as you but well I will definitely keep visiting for more.

Thanks for sharing

Bob Johnson said...

Thanks Claudio, come back anytime

Bryan Younger said...

Like your blog very interesting. Answering your question you left on my blog My father was there for a meeting. He worked at the Oklahoma Department of Transportation for 35 years and they met there once a month.

Bob Johnson said...

Thanks Bryan.

Rose said...

My son wants to get a telescope. Very informative post Bob.

Bob Johnson said...

Thanks Rose

Sherer said...


Its Sherer \m/. very good article. I especially love that book - I have read it about 5 times! Cheers

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