Big Dobson

(Mitch Alsup) wrote in message . com...
"eric" wrote in message ...
Hi,

I would like to know if someone know a telescope maker for 30" or bigger
Dobson (with tracking, navigation system and/or computer control and/or CCD
tracking system). Obsession dont make the 30" anymore, and Starmaster limit
is 28"... cost must be under 35000$US

After a quick survey on the web. If you want a 30"+ scope, you are
probably
going to have to grind and polish it yourself. The only people making
30"+
optics are selling the primary for more than you budget for the whole
scope.

John Hudec tells a story about the 36" optics he made for Obsession.
He tells
about how these objectives just about killed him (in a literal sense),
they
are big, unwieldly, extremely heavy, and easy to damage. In addition,
where
are you going to send it when it needs a new coating?


Thanx for info!
Eric

You should also be aware, that for the most part, a 30"+ scope is for
those
objects you can't reach in a 16-20" scope. You just can't get a short
enough
focal length to get many of the larger sky objects in the lowest power
EP,
nor does the atmosphere put up with the lowest power a 30 throws very
often.
With a 30" F/5 you have a 150" focal length causing a 31mm Nagler to
have
123X minimum power, thereby constraining you observations from 123X to
600X.

You should visit a star party where a 30"+ scope resides (or New
Mexico Skies
and rent the 30"er) to see just how big these suckers are. Hint:
although
the scope can fit in an Excursion sized SUV, the poles will not, thus
man-
dating a trailer of some 16 feet. Nor will the ladder fit in any
reasonable
sized vehicle (to reach the eyepiece/focuser.)

If you haven't do so already, I suggest you start with "The Dobsonian
Telescope" by Berry and Kriege. Reassess you desires and cost
structure,
and then seriously think about building it yourself.

I happen to have a 20"er that I built myself, I wanted to build a
25"er.
I am glad (now 5 years later) that the 20" optic fell into my hands
before
I could find a 25" optic.

Mitch

I have had the good fortune to be able to occasionally view through a
30" Starmaster owned by a consortium here in Northern California. It's
an f/4.5, With a 31mm Nagler, the true field of view is 42 arc-minutes
- not a really wide field, but wide enough for all but the largest
telescope objects. It's true that you need near-perfect conditions to
get the maximum out of this telescope, but even average conditions
provide spectacular views, expecially when it comes to galaxy
clusters, for example.

While it is quite difficult, I have seen one person put it together
and take it down. But it normally requires two people to do part of
these tasks. This particular telescope rides in a small trailer; the
ladder can ride on the roof of the vehicle that pulls the trailer
(depending on who has it at any time).

As for me, I have a 22" that I am happy with and which fits in my
Mazda 323 hatchback, with all the accoutrements.

Clear skies,
Shneor Sherman