Thursday, May 01, 2008


The word “Dobsonian” comes from the world of astronomy. Specifically it refers to an astronomer named John Dobson. Most typically, it’s used to refer to a philosophy of telescope design John Dobson pioneered and popularized. Most generally, it’s used to refer to the overall philosophy of observing, of approaching astronomy, that Dobson promoted. I’m going to be talking briefly about all three usages today.

When I was growing up in McKinley Park on the south side of Chicago, the neighborhood was one of those quiet, safe places where people didn’t lock their doors. My friend and I often set up our telescopes on the sidewalk out front and spent the whole night observing. Now and then people would walk by and stop and ask what we were doing or police cruising past would stop to see what we were doing. We’d always show people Jupiter or Saturn and almost without exception it would be a very cool moment where they’d look through the telescope and their eyes would go wide and they’d look back to the sky as if they couldn’t believe the simple, tiny point of light was actually a beautiful, almost unimaginably large gas giant planet.

That kind of experience is so much fun—introducing people to the wonders of the heavens—that a global phenomenon sprung up a couple of decades back called “Sidewalk Astronomy.” Experienced astronomers, professionals and amateurs, set up telescopes on sidewalks in urban areas and spend the evening showing people celestial wonders.

John Dobson was the guiding light behind this movement. And because “normal” telescopes frequently fail to deliver naked eye views that look anything like what people expect from photographs of the heavens, Dobson completely re-imagined how a telescope could be designed and built so that people would actually see things with their naked eyes that look as beautiful as photographs of the heavens.

Before I talk about Dobsonian telescopes—Dobs, as they’re called—I’m going to review a couple of modern versions of traditional telescopes for comparison.

This is my pick for the best general purpose telescope available in the mainstream market. It’s a reflector telescope with an 8 inch mirror in the classic Newtonian design. It’s been updated, however, as a Schmidt-Newtonian, which means the mirrors have computer-designed surfaces that maximize the field-of-view and overall sharpness. The mount is sturdy, motorized and computerized. This telescope can do a pretty good job of just about anything you’d want to do. You could mount a camera at the eyepiece focus. You could mount a second telescope and camera on the main tube. And although 8 inches is not a very large main mirror, it is large enough to get a reasonably good view of most types of celestial objects. The combination of mount and telescope is probably around 80 pounds, kind of heavy for casual use, carrying in and out, but the weight makes the scope stable.

The other traditional type of telescope is a refractor and this is my pick as the best value refractor in the mainstream market. This is a 4.8 inch telescope. The optics are not the best—note the ad says, ‘not designed for high-power examination of planetary or lunar surface detail’—but for general, wide-angle views of the heaven a scope like this is great. It’s about half the size and half the weight of the Newtonian above (and about half the cost). That makes it easier to casually take in and out for observing. However it will not gather as much light as the 8 inch telescope. Still, this telescope is easy to use, easy to move and will deliver great views of most traditional celestial objects.

Those are two ‘normal’ telescopes. Here is a typical Dobsonian telescope. This is a 12 inch Dob. Dobsonians are sometimes called ‘light buckets’ because the number one design characteristic is their large main mirror. The goal is to have the largest mirror possible to gather the most light. When you look at the heavens through a telescope like this, many celestial sights start to look a little like actual photographs. These telescopes typically contain no electronics of any kind and even the manual parts are usually simplified as much as possible. The whole idea is you point the scope and you look and you enjoy the view.

There are quite a few troubles with Dobsonians, however. In fact, when I was a kid and the topic of Dobs was often debated among observers, I thought they would be a passing fad. [!]

Because Dobs typically have no electronics and simplified mounts, they cannot easily be used for astrophotography. And until very recently the simplified mounts of Dobs made adding computers difficult so if you wanted to point the telescope at something worth seeing, you had to be experienced enough to know exactly where to look or how to ‘star hop’ from one sky location to the next.

Over the years, passionate amateurs have developed ways to do astrophotography through Dobs, but it is still reasonably difficult. Adding computers has become easier also.

What I overlooked as a kid, the reason why Dobs were not just a passing fad, is the amazing views they provide to users. I’ve never looked through a Dob in real life, but user reports are universal that it’s a wonderful experience.

And the simplified construction, the philosophy of designing and building the telescope around visual observing and hand guidance, means that telescopes of remarkable size can be built at reasonably low cost.

For instance, this is a 36 inch telescope [!] an amateur recently built. I was knocked out not just by the large size of this amazing Dob—you have to stand on a ladder to observe—but the builder reports that even though he had experience observing through a 20 inch Dob, his 36 inch scope took him by surprise in one remarkable way. Steven Aggas reports in the June issue of Sky & Telescope magazine: “I thought I’d see the kind of detail that appears in photographs (and I do), but I didn’t expect to see color in the cores of galaxies and other objects. I haven’t begun to push this scope to its limits—I’ve been too busy looking at everything again with my ‘new’ eyes.”

That really caught my attention. Really big Dobs even capture the colors of the heavens.

Hmmm. The leading commercial supplier of big Dob scopes is a company called “Obsession Telescopes.” [Who’d have thought that a guy like me would like a company named ‘Obsession’ . . .] If I ever have the resources, I’m going to think seriously about getting a really big Dob. Seeing the colors of celestial objects with my naked eyes has always been something that I’d considered too magical to ever be real.

I like it when magical things become real.

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