What are the Different Types of Telescopes?

Posted on August 10, 2009

There are 3 main types of astronomical telescope – and it might just turn out that the best telescope for you is the one that looks least like a traditional telescope. All 3 types have the same purpose – to collect light and focus it to a point where it can be magnified so that we can examine it. How each of the different types of telescopes does this is different, and you need to understand the differences as they greatly impact upon what it is you might want to look at, portability, cost and style.

REFRACTING TELESCOPE
These are your classic ‘long tube’ looking telescopes with a big lens at one end and an eyepiece at the other. As the light passes through the curved lens its path is bent (refraction) towards the optical axis of the smaller (objective) lens where it is bought to a focus.
Pros
*Very easy to use
*Require little to no maintenance
*Excel at planetary viewing as they are the best choice for looking at objects that have width e.g. the moon
Cons
*They are heavier, longer and more bulky than the other types
*It is incredibly expensive to make large lenses so they are limited in size and this means less aperture.
*Less aperture means that you cannot get a wide view of the sky and so they are not great for looking into deep space

REFLECTOR TELESCOPE
A Reflector, or Newtonian telescope uses a primary concave mirror that sends light to a secondary flat mirror which reflects the light out a side opening and to the eyepiece where it is magnified and focused.
Pros
*Mirrors cost a lot less than lenses meaning you get more aperture and light gathering power for your money
*Wider aperture makes for better night time viewing and these telescopes excel at viewing faint deep space objects such as remote galaxies and star clusters
Cons
*Can be fragile and sensitive
*May require regular alignment
*Mirrors require complicated cleaning and may require re-coating after several years

CATADIOPTRIC TELESCOPE
These represent the best of both worlds as they utilise both lenses and mirrors to fold the optics and form an image.  They may look the least like a ‘conventional’ telescope but they are right now the most popular type of telescope on the market. The two main types are Schmidt-Cassegrain and Maksutov-Cassegrain.
Pros
*Best all rounder – can be used for planetary, deep space and terrestrial observation
*Easy to use and portable
*Excellent optics and focussing capability
Cons
* They just don’t look like a telescope to most people
* They are more costly than other Newtonians of equal aperture

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How Much Should I Expect to Pay for a Good Telescope?

Posted on August 10, 2009

The good news is that you can get a beginner astronomical telescope in the price range of $100 – $600. As you might expect, the details you are going to be able to see for this price fall far short of pricier telescopes, but you will still be amazed at the detail you can see of the moon – craters and mountains you just did not know existed. As a rough guide to prices you should expect to pay around $5,000 for an 8 inch Refractor and $500 for an 8 inch Reflector. The big price difference is due to the fact that Reflectors use mirrors and these are a lot cheaper (albeit a nuisance to maintain) than the lenses in a Refractor telescope. A Catadioptric will fall somewhere in between and you should expect to pay $1,000 for an 8 inch telescope.

Given that refractors look the most like the traditional image of a telescope these are historically what most people bought to begin with, but given the staggering increase in price as you increase in aperture (lens size) the standard entry scope is about 2.4 inches. After a while with one of these the next choice for budding astronomers was a 6 – 8 inch Reflector. The Orion Starblast 6i Intelliscope Reflector (with computerized object locator) will you set you back just under $400. Go up to a 10 inch Reflector and expect to pay around $1,000.

Nowadays most people get started with a Catadioptric telescope as they provide the best option in terms of versatility and performance. They sit in the middle price range of the three telescope types meaning that you will have to pay more than for a Reflector of the same aperture, but in my opinion it is worth it. A Schmidt-Cassegrain with a decent 8 to 9 inch lens will cost somewhere in the region of $800 – $2,000. If you are determined to see deep space objects then ideally you are going to want an 11 inch lens and these will cost you somewhere in the region of $3,000 – $4,000. A Celestron EdgeHD 1100 CGEM SCT from telescope.com would currently cost you $3,499.

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Where Should I Buy a Telescope?

Posted on August 10, 2009

The chances are you are not going to have a decent telescope store on your doorstep, or even close – they are few and far between. You may find some to buy in a local toy shop, but I would not recommend it, in my opinion you should also avoid purchasing at superstores or department stores like Wal-Mart and K-Mart. If you don’t want to be disappointed then you will need a good product from a good manufacturer. Avoid any telescope that puts magnification as its main selling point and avoid mass marketed 2.4 – 4inch junk refractors. The telescopes that some stores just get in at Christmas time are generally not that good so try to avoid those as well.

You could buy via direct mail but make sure you research the company and the telescopes on offer before you part with your money. Magazines such as Sky & Telescope will provide you with some decent offers but unfortunately you only tend to get a one line description which is a bit limiting. If you have an astronomy club near to you then paying a visit is a great way to see some telescopes in action and get some recommendations. On-line is a great way to go and I’ve always used and recommended Telescope.com, with 20 years experience in the telescope business they definitely know what they are doing.

If you stick to a top brand telescope from a reputable specialist provider then you shouldn’t go wrong, and if your new telescope turns out not to be right for you then generally you will be able to send it back.  My current brand recommendations are Celestron and Orion.

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