Reflections on the Dobsonian Telescope

Today I am remembering the great gift of astronomy that came to all of us from John Dobson, the inventor of the Dobsonian telescope. John died yesterday at the age of 98.

During my lifetime, one of the most profound developments in the technology of telescopes was made by John Dobson. In 1968 telescopes for non-professionals were either cheap and crummy, or precision optical and mechanical devices that were either very expensive, or required a sophisticated workshop to construct. Telescopes with a main lens that was more than 8 inches in diameter were almost too heavy for one person to carry, and they were beyond the means of most. Dobson changed all that.

John Dobson had a passion for showing people the sky. He founded the San Francisco Sidewalk Astronomers. And to see some of the great celestial celebrites, he realized observers needed a huge telescope. His discovery, and invention, was that if all you wanted to do was have an awesome nighttime view of galaxies, nebulae, and other wonders, you could strip away most of the technology that professional astronomers must have, and make a telescope with only a big glass lens and a few sheets of plywood. The cost was mainly that lens.

While I call this an advancement in technology, most of what he did was simplify the construction of a telescope, and re-think how it would be used. One of his (many) breakthrough discoveries had to do with the telescope bearings. He found that if the ‘scope moved by Teflon sliding on Formica, the coeficient of sliding friction was the same as the coeficient of starting friction. What that means is that if you have a telescope with no clock drive (to follow the stars), and had to push it by hand to keep the highly magnified target in the eyepiece, with Dobson’s bearings, the telescope would move smoothly and stop smoothly.

In 1985 a group of us build a Dob with a 17-1/2 inch mirror to be able to observe the return of Comet Halley. At the time, it was the largest telescope in Manitoba (in terms of the size of the lens). Here is the story of a group of us having our first glimpse of the Comet Halley. In the months that followed, thousands of people observed the comet with that telescope.

That Dobsonian telescope is now here on Bowen Island.

A group of people on Bowen Island observing Mars with the 17-12 inch Dobsonian telescope

A group of people on Bowen Island observing Mars with the 17-1/2 inch Dobsonian telescope


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