SDM Telescopes
15-32 inch custom built Obsession style Dobsonians
 

 

The History of the Dobsonian Telescope

Sometime in the late 1970’s John Dobson invented a type of telescope mounting. This was driven by necessity and his lack of resources. Cheap materials were relied on the build a telescope that resembled a cannon and used large bearings of Teflon and Formica to move the optical tube assembly up and down. A full history of this is available at the Sidewalk Astronomers web site.

This “altaz” type of telescope mounting had a rich history, as William Hershel had built such telescopes with wooden mountings. The original Dobsonians were made with cheap junky materials, generally plywood with a cardboard tube. The spider, secondary mirror holder and primary mirror cell was made from wood. The mirrors were fashioned, in rapid fashion, from plate glass. This design was copied widely in the 1980’s, and there was a proliferation of larger reflecting telescopes using this design and made from these materials. This design allowed a considerable number of amateurs to afford a larger aperture telescope.
 



An early dobsonian.

A commercial vendor, Coulter Optical of California, soon used the design to sell a line of reflectors. Coulter offered a 13.1 inch, 17 inch and 29 inch telescopes. They also sold just the optics, which allowed amateur telescope makers to build their own. This was the start of what has been called the "Dobsonian Revolution", where large aperture alt-az telescopes became the weapon of choice amongst visual observers of the sky.



Coulter Optical's 13.1 inch with blue livery.

This became one of the first "dobsonian" telescopes available for the amateur market.

Whilst the dobsonian provides large aperture in a transportable form, these telescopes were still very heavy and awkward to move. What changed this was the publication, in Telescope Making magazine issue 17 in 1981, of Ivar Hamberg’s truss tube alt-az telescope. This design, whilst still using Teflon on Formica bearings, was totally different. It was designed to be taken apart for transport to dark sky locations, and used a modified truss design. They are still called Dobsonians, but bear as much relationship to Dobson’s design as the VCR does to DVD. Almost all large modern alt-az mounted telescopes of over 12.5inch aperture today copy this design, which has been considerably refined by David Kreige. Dave has put an enormous amount of thought and effort into this design to make it relatively inexpensive and user friendly.

Ivar’s article in TM#17 introduced the collapsible truss tube, allowing disassembly and transport to dark skies from urban areas. This opened up a whole new field of large aperture deep sky observers, a whole new trend.



Ivar’s 17.5 inch telescope that started it all



A modern Kreigescope type Obsession, built by Peter Read of Victoria.

Ivar’s design has been further evolved to some ultra light designs to reinforce this trend. One of these is the Bobroff design, seen some years ago at Queensland Astrofest. Yet Ivar is almost forgotten. They are not called “Hambergians”’, but universally “Dobsonians”. Interestingly, Dobson himself is quoted as not being in favour of the name.

It is worth noting that the “Dobsonians” owes a lot to:

  1. Sir Isaac Newton, who invented the optical system.

  2. Leon Foucault, who designed an optical test to produce a paraboloidal.

  3. John Dobson, who was first with Teflon on formica bearings.

  4. Ivar Hamberg’s truss tube alt-az telescope design, and

  5. David Kreige, who refined this design in his Obsession line of telescopes.

References:

TM magazine issue 17.

http://web.telia.com/~u82002652/Galaxies/Obs/Dobson.htm

WRP


"Size DOES Matter"

 [Home] [Web Shop] [About SDM] [Scope Showcase] [Big Dob Prices]
[The Workshop] [Links] [Articles] [Extras] [Contact SDM]