by Will Kalif

Dobsonian telescopes have revolutionized amateur astronomy by making large and powerful telescopes available at very reasonable costs. If you are considering buying one this guide will help you make the choice that is right for you.

What is a Dobsonian telescope and why is it so different?

This type of scope was invented by John Dobson and introduced to the world in the 1970’s. The tube assembly is exactly the same as a typical Newtonian scope but it varies radically in the mount assembly. Instead of an equatorial mount (which is expensive and awkward to use) it has a simple box on a rotating base. This assembly brings the cost down and makes it very easy to use.

Why are they so good?

There are three very distinct advantages to this type of telescope. The first advantage is cost versus light gathering power. An eight inch scope of this type will typically cost you less than half that of a traditional eight inch newtonian and a quarter that of a folded optic style telescope. And if you buy an eight-inch refractor the cost balloons up to typically over ten times that of a Dobsonian.

The second advantage of this type of scope is ease of setup. They generally come in two pieces that are the tube assembly and the base assembly. You place the tube on the base and you are ready to go after an easy collimation check and adjustment.

The third advantage is portability. This portability is relative because if you are going to be using a ten or twelve inch dobsonian it still is a bit of work to get it out of the house and into the car. Compared to a standard Newtonian or refractor though it is much easier and much lighter. But it is typically not as convenient as a folded optic style scope. Which is designed to be portable - but at significantly higher cost.

What are the trade-offs?

There are some sacrifices you make with this type of telescope and the first is the difficulty with taking photographs. To take astrophotos you need a telescope that will move perfectly across the night sky with a motor. This allows to you take a long exposure of celestial objects. Because the Dobsonian uses an alt-azimuth style mount it is not conducive to this. So if you are intending to take photographs through your scope this might not be the right choice for you. They also tend to be a bit heavy and are typically heavier than folded optic style scopes. If weight is a consideration you should try to go to a store that displays telescopes so you get a hands-on feel for them.

Which size should you get?

This type of scope typically is manufactured and sold at retail with mirrors ranging in size from four and a half inches to twelve inches in diameter.

Which size you get is a matter of personal preference but I do have some guidelines you might find useful. Typically I recommend a solid place to start is with an eight inch telescope. This size has tremendous light gathering power and it will give you an unending list of night sky object that you can see in wonderful resolution. If you are really not sure about the hobby and have never used one you might want to go a bit smaller to the six-inch size; it’s a good entry point for getting your feet wet while keeping the cost down. I don’t recommend you purchase a four and a half inch model. You don’t reap either the cost benefit or the size benefit. The ten-inch or larger models should not be your first purchase. They take some effort and you should be versed in the hobby or spend some time with someone who already owns one before you make the commitment. The twelve-inch models are stunning, and will reveal many secrets of the universe to you, but can be difficult to transport or even get in and out of doors and cars.

Who should you buy from?

I recommend two manufacturers of telescopes. They both have been making instruments for a long time and each has a great line of Dobsonians. They are Celestron and Orion. If you want the absolute biggest telescope aperture you can get for the absolute lowest price, no frills, yet high quality optics, you should take a look at the Celestron line. If you want more options or computerized addons that will help you find objects in the sky then you should consider the Meade line. Meade also makes some wonderul truss style scopes in the larger versions that make big telescopes easier to set up and transport.

Dobsonian telescopes have opened up a whole world of deep space amateur astronomy to the casual observer by making big telescopes very affordable. And with a little bit of thought and research you can find the one that is right for you.

The Meade Telescope was first created in 1972 with the idea of designing telescopes and accessories that everyone, from beginners on up could use to enhance their knowledge and understanding of the skies. In 1977, the company designed and manufactured its first two “in-house” models-reflecting telescopes and offered them to the public. When the orders poured in, they quickly became aware that they had not made enough and all orders were put on back-order. The company offered the eager Meade telescope customers a refund in a hand-written note explaining the situation. Since that time, they have remained one of the top telescope manufacturing companies in the world.

If you are a beginner, you may be wary of purchasing your first telescope. The prices range from under fifty dollars to the thousands. A good beginning telescope like the Meade telescope will have all of the basic functions and be easy to operate even for the most inexperience astronomer. The most basic telescope in the Meade family is the Meade DS-2130ATS, which is a reflective telescope (uses mirrors to gather light and reflect images) and it offers very good clarity and detail.

The NG/NGS Series offers a reflective Meade telescope with computer capabilities and a manual mount that makes it easy to move and adjust. Another beginning level telescope is the AZ series. These are refractor telescopes (use curved glass lenses to collect light and images for viewing) that are great not only for deep space viewing, but also for terrain on the earth. The final series in the Meade Telescope family is the EQ series. These telescopes have large apertures for the best quality viewing. Aperture is the most important factor in how well a telescope can collect and display images.

You can find 12 different series in the Meade Telescope line of beginner and specialty scopes. They also have kits for those who want to personalize their scope for their needs. For instance if you would like to view earth terrain, or if you are interested in space photography there are kits that you can order with all of the Meade telescope equipment you will need in the kit. They have special lenses and other accessories like mounts, stands, and so on and so on. They make it very easy to get into the astronomy hobby at any price level. Check out the reviews and their site to make the most informed choice.

by Eriani Doyel

In 1975, the Orion Telescope Company began as a mail order catalog company offering telescopes for both new and seasoned astronomers. They joined with the Imaginova Company in 1999 to better serve their customers and market their product.

Orion offers telescopes but they also sell binoculars for all types of outdoor enthusiasts. If you visit their site you will find customer support, same day shipping service, binoculars and telescopes to fit every budget and need, and information to help you to make your Orion Telescope purchase. Orion offers five different types of telescopes for your viewing pleasure:

1. The reflector was one of the first telescopes invented. It was originally called the Newtonian, after Sir Isaac Newton who produced the first model. It uses a series of mirrors to focus and reflect the image back to the eye. The reflector is generally better for deep sky viewing.

2. Orion Telescope also produces another good beginner scope in the refractor scope. This scope uses curved glass lenses to reflect images in the night sky. It is ideal for looking at individual planets, stars, the moon, etc. and gets crisp, clear detail.

3. The Cassegrain telescope is known for its portability and its ability to look at images both on the ground and in the sky. It is one of the Orion Telescope line that is most adapted to be taken out on hiking or camping trips.

4. Spotting scopes are a product which is similar in nature to binoculars. They are much like the telescopes you might have seen on the old pirate movies except they are not usually made in gold anymore. This is another highly portable member of the Orion Telescope family and the images are seen upright unlike many telescopes that invert images. They are great for horizon level viewing.

5. Dobsonian scopes are refractor telescopes that have a very low base and can be used on a table top, on the ground or any other fairly flat, even surface. They are good for beginners who may prefer the point and view method of using an Orion Telescope.

Take a look at the Orion Telescope line. Not only do they offer a wide variety of products with accessories to help you, and enhance your viewing experience, they have information that will help you to decide which if any of their products is right for you. Professionals and beginners alike may find something that may appeal or interest them.

Basic Telescope Designs

The job of a telescope is to collect light, not to magnify an image (the eyepiece does that job). The larger the objective (the part that collects the light) whether it be a lens, in refractors, or a mirror, in reflectors, the more light the telescope will collect. The more light you can collect, the more detail you will be able to capture, and also important for astrophotography, the shorter your exposures will need to be to capture this detail.

Refractor Telescopes

The type of telescope most people visualize when they hear the word telescope is the ‘Refractor’. This is what Galileo used for his break-thru discoveries. A refractor has an objective lens at the front which passes the light straight through to the back of the tube, focusing this light at an eyepiece or for astrophotography a camera.

Advantages:

-No central obstruction (see more in the reflecting scopes), giving higher contrast.

-Due to the simple design they require little maintenance.

-Excellent for planetary and lunar viewing and photography.

-Excellent for wide field viewing and astrophotography especially in shorter focal lengths (more on this later).

-Because the objective is permanently mounted and aligned there is no need for collimation (again more on this in another article).

-Excellent color in apochromatic and ED (Extra Dispersion) designs.

Disadvantages:

-Costlier per inch of aperture (objective) than reflectors and catadioptric telescopes.

-Can become bulky and difficult to manage, especially in larger lens designs.

Newtonian Telescopes

This design was invented by Sir Isaac Newton (he of the apple on the head fame). Instead of a lens at the front of the tube this telescope design uses a concave, parabolic mirror to collect light reflecting it back towards the front of the tube to a flat diagonal mirror which reflects the light out the side of the telescope to the eyepiece or camera for astrophotography.

Advantages:

-Lowest cost per inch of all the telescope designs.

-More light gathering power per dollar because of the lower cost design.

-Absolutely perfect color rendition.

-More compact design compared to a refractor of similar light gathering ability.

-Excellent contrast for planetary and lunar astrophotography and viewing in longer focal lengths.

-Can get excellent wide-field astrophotos and short exposures in shorter focal lengths.

Disadvantages:

-Slight loss of contrast due to the central obstruction (the flat secondary mirror) as compared to a refractor.

-Requires more maintenance, such as collimation (discussed in another article) which is vital for great results in your astrophotography, although you will learn how to do this quickly with practice.

Schmidt-Cassegrain Telescopes

This is a very popular design, with a high tech look. Also known as a CAT (Catadrioptics). They use a combination of lenses and mirrors to collect and focus the light onto the eyepiece or camera. The light enters the telescope through a thin ‘lens’ called a schmidt corrector plate, goes to the back of the scope to a spherical primary mirror which reflects the light back towards the front. Here the light strikes another mirror, the secondary mirror which is mounted on the corrector plate. This secondary mirror then reflects the light back towards the back where it is focused onto a hole in the primary mirror where the light is collected by an eyepiece or your astrophotography camera.

Advantages:

-Compact and portable.

-Low maintenance although once again collimation is required for top performance.

-Many, many astrophotography accessories available.

-Cheaper per inch of aperture as compared with refractors.

-Excellent all-round telescope, good to very good for both visual and astrophography.

-Very good for planetary and lunar viewing and astrophotography.

-Very good to excellent for DSO (Deep Space Object) astrophotography with a caveat (see the disadvantages).

-Very good to excellent optics, both Meade and Celestron are putting out excellent optics on a consistant basis.

Disadvantages:

-Costlier per inch of aperture as compared with Newtonian telescopes.

-Loss of contrast due to the central obstruction which is even larger than that in the Newtonian scopes.

-Due to their longer focal lengths the field of view is smaller and longer exposures are required for astrophotography, although a lens known as a focal reducer is available which minimizes or removes this problem. The longer focal length is actually an advantage in planetary and lunar photography.

Maksutov-Cassegrain

The Maksutov-Cassegrain telescope design is basically the same as the Schmidt-Cassegrain design except it uses a meniscus lens at the front instead of a Schmidt corrector plate. The main advantage to the Mak telescope design is you will get sharper higher contrast planetary and lunar images when compared with the Schmidt design.