The forgotten man of telescope making

Chris L Peterson wrote:

Maybe, but it was just another technical adjustment. We remember
Serrurier for the truss design itself

A funny thing, but 90% "remember" Serrurier trusses wrongly. The
Serrurier truss extends from the pivot to the secondary, and another
truss extends from the pivot to the primary, balancing deflections and
keeping the planes of the primary and secondary aligned.

Just sticking poles on the primary box, doesn't make it Serrurier trussed

Steve

On Sun, 20 Feb 2005 16:37:45 +0000, Steve Taylor
wrote:

A funny thing, but 90% "remember" Serrurier trusses wrongly. The
Serrurier truss extends from the pivot to the secondary, and another
truss extends from the pivot to the primary, balancing deflections and
keeping the planes of the primary and secondary aligned.

Just sticking poles on the primary box, doesn't make it Serrurier trussed

No, it doesn't, and I didn't mean to suggest that all such designs
utilize Serrurier trusses. But Serrurier really developed the concept of
using a truss to support the secondary, and is rightfully remembered for
this- not unlike we call a certain class of mount Dobsonian even if it
doesn't utilize any of the materials popularized by John Dobson.

Serrurier developed his system for equatorial telescopes, which are much
more difficult to design than altaz telescopes. Simpler truss systems
are possible if gravity is only operating on one axis of the scope.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

One thing, the home telescope builder still, for the most part, follows the
Dobsonian way, my Babylon 8 which came to be with the help of many others is
a soild tube Dobsonian that has a bit of a mod so it's eayer to use for
Sidewalk Astronomy.
I know I've read of and seen home made truss scopes too, and as others have
said, I've never heard of the one you posted about. There's one small
company right here in Calif. I wish I could win the Lotto, as then I could
afford to have them make me a verson of their design to fit my B8's mirror,
it's a cross between closed tubes and truss, as it's a framework that has
two sections, one that slides into the other for transportaion. Hay they are
in the FAQ too. But until that day comes, I use my B8, it might not be as
good as it could be, but I was the only one to do the hands on work of
building it and it's the best I could do.

As far as the store bought scopes go, the soild tube Dobsonian still in the
number one type of scopes sold and can be found very easy.

--


SIAR
www.starlords.org
Telescope Buyers FAQ
http://home.inreach.com/starlord


"StarDust" wrote in message
...
Sometime in the late 1970's John Dobson invented a type of telescope. This
was driven by necessity, in that cheap materials were relied on the build
a
telescope that resembled a cannon and used large bearings of Teflon and
Formica.

On Sun, 20 Feb 2005 20:11:01 +1100, "StarDust"
wrote:

Sometime in the late 1970's John Dobson invented a type of telescope. This
was driven by necessity, in that cheap materials were relied on the build a
telescope that resembled a cannon and used large bearings of Teflon and
Formica.

It could be argued that Jean Texereau had a kind of "Dobsonian"
design in his book. It consisted of an alt-az mounted square
Newtonian tube, with a rod that could lock it in place in altitude.
I think that pre-dated the Dobsonian.

Trusses were about in the 70's. There was a driving force of
desperation about not having readily available tubes in large enough
diameters.It was decades before cardboard concrete form-tube reached
Europe and it is still not widely available. I made an 8" "truss"
myself using expanding rubber wall plugs to hold the alloy
(ex-radio-aerial) tubes in place on the plywood rings.

The difference Dobson made was in providing a cheap and practical
bearing for amateur telescope mountings where nothing else existed
before. Except for expensive shafts and pilow-block bearings. His new
concept allowed a silky, no-backlash movement without shake that had to
be experienced to be believed.

Using shafts and bearings you had to add a sticky clutch to stop the
scope wandering all over the sky. He also introduced the concept of
thin mirrors and larger apertures than had been the norm. A 12" scope
was considered a very large amateur telescope before Dobson broke the
mould. Particularly in Europe.

Later mods to the basic Dobsonian design come from those standing on
the shoulders of Dobson. Dobson was the giant in amateur telescope
making history as far as I'm concerned. His design came out of
necessity. Throwing money at a problem is always far easier than doing
it cheaply. And still doing it incredibly well!

Thank goodness for the TM magazine! Which spread the Dobsonian world
and offered real, hands-on advice on amateur contruction. I suppose you
had to have been there to understand. There was really nothing like it
before TM magazine.

I seriously doubt if today's commercial telecope production worldwide
would ever have taken place without Dobson stimulating interest in
telescopes and astronomy amongst a wider audience. It's all down to
Dobson making it affordable instead of strictly toys for the middle
classes. The competition to provide affordable telescopes to match
those that people were making themselves must have forced prices down
in the long run. You only have to look at the price difference, then
and now, that seems to completely ignore inflation over the intervening
decades.

Regards
Chris.B

What's a "DOB"?

wrote:
What's a "DOB"?


See: http://en.wikipedia.org/wiki/Dobsonian

Dah, I thought it twas-erst a Newtonian in a box.....


"Sam Wormley" wrote in message
news:W_rSd.39251$4q6.17215@attbi_s01...
wrote:
What's a "DOB"?


See: http://en.wikipedia.org/wiki/Dobsonian

StarDust wrote:
Sometime in the late 1970's John Dobson invented a type of telescope.
This
was driven by necessity, in that cheap materials were relied on the
build a
telescope that resembled a cannon and used large bearings of Teflon
and
Formica.

First of all your timeline is off by at least 10 years, check your
facts.

I owned such a telescope, a 13.1 inch dobsonian sold by Coulter
Optical back
in the 1980's. It was a beast, and was almost impossible to move.
Coulter
also sold 17.5 inch and 29 inch Dobsonian models in blue livery.
Their bulk
is the reason that I don't see any Dobsonian telescopes around today.
There
was a brief period when there were many such telescopes being made,
as
recorded in the pages of the now defunct TM magazine. They were made
of
plywood or chipboard, with a tube of cardboard. This design allowed a
considerable number of amateurs to afford a larger aperture
telescope.


Why would you buy something you had trouble moving? Sounds like you
need to hit the weight room to me.

Tube-based designs 12" and larger are still offered by Meade,
Discovery, Celestron, Hardin Optical and Orion. There are probably
others too. I have seen many 12.5" tubes out in the field, and a few
larger ones. Tube-based designs are preferred for scopes less than 12"
due to their superior performance/cost ratio. Under 12", weight and
size are not as critical.


What changed this was the publication in TM issue 17 in 1981 of Ivar
Hamberg
's truss tube alt-az telescope. Despite them being called Dobsonians,
they
bear as much relationship to Dobson's design as the VCR does to DVD.
Almost
all modern alt-az mounted telescopes these days copy this design,
which has
been considerably refined by David Kreige. These Kreigescopes are
called
"Obsessions".


Poor analogy, a better one would have been "DVD to CD-ROM". For large
apertures trusses are superior in many respects, but are also more
complex, require more setup time and cost more.


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


Ivar's design has been further evolved to some ultra light designs to
reinforce this trend.

Yet Ivar is almost forgotten. They are not called "Hambergians". His
contribution is almost forgotten. Why? Is it that Dobson is a citizen
of the
USA whilst Ivar is from Stockholm, Sweden? Is there a jingoistic bias
here?
Does everyone really think that Ivar's design is really just another
Dobsonian, just because it uses an Alt-Az mounting, just like
Herschel used?
I don't think so. I think Ivar needs a bit more recognition than what
he is
currently given.


With due respect to Mr. Hamberg, "John Dobson" rates almost 36,000 hits
on Google vs. 517 for "Ivar Hamberg". It's obviously another case of
pro-American bias. Case closed, find something else to whine about.

"Mark" wrote in message
ups.com...

StarDust wrote:
Sometime in the late 1970's John Dobson invented a type of telescope.
First of all your timeline is off by at least 10 years, check your
facts.

So it was the 1960's!!!


I owned such a telescope, a 13.1 inch dobsonian sold by Coulter

Why would you buy something you had trouble moving? Sounds like you
need to hit the weight room to me.

I believed the ads in S&T........


With due respect to Mr. Hamberg, "John Dobson" rates almost 36,000 hits
on Google vs. 517 for "Ivar Hamberg". It's obviously

and George Bush is President.
Your point being?
is history a popularity contest?


another case of
pro-American bias. Case closed, find something else to whine about.


It's not a whine. Just documenting the facts.