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The 'Dobsonian'

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The 'Dobsonian' was created by Frank Ryan

With regard to the 'Dobson' or 'Dobsonian' telescope.
Can anyone enlighten me as to why I see this this
design constantly refered to as 'Radical' or ' Revolutionary'.
To me it's a DIY Newt.
Was John 'D' really the first person to knock one of these together?
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16 years 1 month ago #36912

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Replied by dave_lillis on topic Re: The 'Dobsonian'

Before John D, nobody had thought of putting one of these scopes on a rocker box, hard to believe isnt it!, they were always expensive high end eq mounts, he popularised it and made big newtonians very affordable as the dob mount it just a few pieces of wood.
Maybe other before his did make them, but his is the name that stuck.
Dave L. on facebook , See my images in flickr
Chairman. Shannonside Astronomy Club (Limerick)

Carrying around my 20" obsession is going to kill me,
but what a way to go. :)
+ 12"LX200, MK67, Meade2045, 4"refractor
16 years 1 month ago #36915

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Replied by Frank Ryan on topic Re: The 'Dobsonian'

Ahh right so It wasn't really the scope...
it was the mount.
Yes!
it is really hard to believe that no one
'copped' on to it eariler.
It would make you think...
what else is there looking us in the face...waiting for an Eureka! moment.
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Meade ETX-125PE, Bresser 10 x 50 Binos & Me Peepers
16 years 1 month ago #36924

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Replied by TrevorDurity on topic Re: The 'Dobsonian'

And even more amazingly he got no royalties for it.
Though the first guys to commercialize the design (I think I read it was Coulter Optics) did give him credit for the idea.
16 years 1 month ago #36930

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Replied by jhoare on topic Re: The 'Dobsonian'

John Dobson is on record as saying that he didn't want royalties, he wanted his fellow astronomers to be able to afford bigger apertures and those who couldn't afford to buy a traditional telescope setup to have a cheaper option.
John

Better that old people should die of talk than to have young people die in war.
16 years 1 month ago #36933

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Replied by mjs on topic Re: The 'Dobsonian'

Ahh right so It wasn't really the scope...
it was the mount.


To be exact it is the telescope as well as the mount. The true Dobsonian telescope includes a relatively light-weight (compared to traditional Newtonians), self ground mirror with most of his original mirrors being made from salvaged ship porthole windows.
The whole design is a great example of "the simpler the better".
Many of us had the pleasure of meeting him in person at the WSP a couple of years back. What an inspiration he is.....
16 years 1 month ago #36934

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Replied by albertw on topic Re: The 'Dobsonian'

To be exact it is the telescope as well as the mount. The true Dobsonian telescope includes a relatively light-weight (compared to traditional Newtonians), self ground mirror with most of his original mirrors being made from salvaged ship porthole windows.


Though the rocker box does work with heavy 10" Schmidt Newtonians!


Never heard about the portholes before!
Albert White MSc FRAS
Chairperson, International Dark Sky Association - Irish Section
www.darksky.ie/
16 years 1 month ago #36935

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Replied by Frank Ryan on topic Re: The 'Dobsonian'

salvaged ship porthole windows

Wow! - Really?
How did they get them to reflect evenly (parabolicly?)
Did they silver them as well?

So are these scopes easy enough to make?.....
(Hmmm...Bad weather project maybe)


Albert...
it's funny....
That is the mental picture I had of what my new 'Lidl' LXD
would end up like!
:)
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16 years 1 month ago #36937

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Replied by pmgisme on topic Re: The 'Dobsonian'

There is a saying in Engineering circles:

"The Great Engineer Simplifies things, the Bad Engineer makes things more complicated."

Nowhere is this principle more true than in the ingenius design invented by John Dobson.

Sometimes the greatest inventions look "obvious" AFTER they have been invented.

John Dobson's name will live on in the Hall of Fame of telescope designers.

One of these days I expect to be able purchase a top-quality 20" telescope which is easy set up and to use and with which gives rock steady views even at high magnifications....For LESS than the price of an old second hand banger.

Thank you John Dobson,genius.

Peter.
16 years 1 month ago #36938

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Replied by mjs on topic Re: The 'Dobsonian'

Quote:
salvaged ship porthole windows

Wow! - Really?
How did they get them to reflect evenly (parabolicly?)
Did they silver them as well?


To clarify, he used the glass form two porthole windows to grind and figure one into a parabolic shape that was then "silvered" by a coat of aluminum (usually).
16 years 1 month ago #36947

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Replied by mjs on topic Re: The 'Dobsonian'

Though the rocker box does work with heavy 10" Schmidt Newtonians!


Nice sturdy looking mount Albert. One thing I found with my first home built dobsonian was that with the focuser mounted like yours made it difficult to balance.
When pointed at the Zenith the weight of the eyepiece would cause it to creep past the zenith. I use the focuser at 45 degrees to eliminate this and moved the altitude bearings a little (10mm) above the tube center to also help balance the finder, etc.
16 years 1 month ago #36948

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Replied by jhoare on topic Re: The 'Dobsonian'

With a longer tube or with an additional platform under the rocker box to give it more height it might be practical to have the focuser axis parallel with the azimuth access. That would cancel the balance problem.
John

Better that old people should die of talk than to have young people die in war.
16 years 1 month ago #36957

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Replied by mjs on topic Re: The 'Dobsonian'

With a longer tube or with an additional platform under the rocker box to give it more height it might be practical to have the focuser axis parallel with the azimuth access. That would cancel the balance problem.

True that is the ideal placement for balancing but I found that a bit uncomfortable to use on objects near the horizon. :cry:
16 years 1 month ago #36974

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