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.