Sonotube vs. Metal for a 8" or 10" telescope..
Anybody know whitch is really better for the tube for a reflector?

They are different, advantages to each.

Thermally I think the sonotube is superior,  the metal is more prone to tube
currents, when the night is cool and the scope equillibrated, just touching the
metal tube for a moment will setup a tube current.

On the other hand, the metal tube looks a lot slicker.

But the bigger question concerns the rest of the stuff that comes with the
different tubes, optics and mechanicals.

Those metal tube DOBs come with the "Correct Tension" or "Springy Things" and
those really do work quite nicely.

jon

A friend of mine, Bob Mulford, has built a lot of Newtonians and played
quite a bit with different types of tubes.  His choice is unpainted
aluminum, and his experience has convinced me that my next Newt will have
this type of tube.  (This choice has also worked very well on my refractor.)

Sonotube works well.  It has the advantages of being easy to obtain and easy
to work.  The disadvantages include weight and the need to protect it from
moisture.  It has a fair amount of mass and is not a good conductor, so it
does not give up heat quickly.

Aluminum cools quite well, since it is a good conductor.  If you paint it,
it is also a good radiator (unless you pick a paint with low emissivity),
which is not necessarily a good thing.  The optics in my wife's painted
aluminum 6" f/8 had dewing problems.  The secondary almost always dewed
over, and even the primary would dew over on some nights.  I had to cork the
inside of the tube to prevent this.

Unpainted aluminum does not radiate well, so it is unlikely to cool down
much below ambient air temperature, minimizing tube currents and eliminating
the chance for the optics to dew over.

Although we use telescopes at night, many folks believe they should look
nice.  Unpainted aluminum is not very attractive.  You can wire brush it, or
you can put a "jeweled" finish on it.  If you want to see an example of
Bob's "jeweled" finish on an 8" scope visit
www.stellafane.com - go to 2002 Post-Convention, and PHOTOS OF ALL THE
'SCOPES ENTERED
IN THE 2002COMPETITION, Page 3 of 5.

Sonotube was nice when it was hard to get suitable aluminum tubing, but such
tubing is much easier to get these days.

Clear skies, Alan

Jon,

Folks seem to like using flocking material in Newts, and a layer of it or
something similar on the inside of an aluminum tube reduces this problem,
and may well eliminate it.

Clear skies, Alan

One thing I love about my steel tube dob is I can hold stuff on it with
magnets.  Speaker magnets also make great counterweights.

http://home.earthlink.net/~tomhole/xt1018jullabeled.jpg

Everything else mentioned is germain.  They sure do get cold in the snow.

Clear skies,

TOm

I just wear gloves, seems to do the job quite nicely.   When it is warm there
doesn't seem to be a problem.  

jon

Jon,

Alas, much of our observing is done under rather cold conditions.  I hate it
when we have to worry about frost instead of dew <g>.

Clear skies, Alan

JOOOOOON!!!

GLOVES?  It gets cold enough there for gloves?  I thought it stayed a
constant 68 degrees 24/7/365 in San Diego...  {;-)

--
To reply, remove the "z" if one appears in my address

I think 68 is when they put on gloves and coats in San Diego.  You should
see the folks in the Florida Keys when February is a bit on the cool side
<g>.

Clear skies, Alan

One thing I like about my sonotubed Meade Starfinder is that after it's
taken on a few scuff marks and scraps, the tube is easily repainted.  I
recently repainted mine a very nice and extremely glossy black.  It's so
shiny that from just a few feet away it could pass for metal.

Also, I have owned various sonotubed scopes for more than 20 years and have
never found moisture to be a problem for the tube.  Of course, this is when
they are properly coated and all exposed "paper" edges (like the opening on
the tube which the focuser mounts over) are sealed.  This is easily done
with a coating of white glue applied with the fingertip.

Martin

My Babylon 8  8inch F8 dob is sonotube, I don't need to worry about the tube
being hot if left out in the sun, or on a cold witer night having fingers freeze
to it.

--
"In this universe the night was falling,the shadows were lengthening
towards an east that would not know another dawn.
But elsewhere the stars were still young and the light of morning
lingered: and along the path he once had followed, man would one day go
again."

                       Arthur C. Clarke, The City & The Stars

SIAR
www.starlords.org
Bishop's Car Fund
http://www.***.com/
{*filter*} Writers Shop
http://www.{*filter*}writtersshop.netfirms.com
Telescope Buyers FAQ
http://www.***.com/

For the open edge of my dob, I soaked SUPER GLUE into it. Now a NUKE will bounce
off it.

--
"In this universe the night was falling,the shadows were lengthening
towards an east that would not know another dawn.
But elsewhere the stars were still young and the light of morning
lingered: and along the path he once had followed, man would one day go
again."

                       Arthur C. Clarke, The City & The Stars

SIAR
www.starlords.org
Bishop's Car Fund
http://www.***.com/
{*filter*} Writers Shop
http://www.{*filter*}writtersshop.netfirms.com
Telescope Buyers FAQ
http://www.***.com/

Cute, but we often travel to Arizona, we seem to like Monument Valley for New
Years, gets a bit chilly up there around that time.  <g>

During the winter it gets cool up in the local mountains, even in the city
sometimes it gets into the 40's!  

Tough life..

jon

My 10" GS Dob is metal but silver colored .. which does keep it cooler
if I leave it out on the patio during the day.

My 10" Coulter Dob of ten years ago is gone. It used a sonotube, which
was fine. But the base was really poor; it fell apart and I had to
rebuild it.  I like the mechanics of the new GS Dob much better, and the
optics seem as good -- and the focusser is great (had to replace the one
on the Coulter immediately).

Phil

My vote is for Sonotube, the weight of my aluminum (8" mirror) tube gets
old as I do remove it from the equatorial mount when storing.  I have not
noticed any problems with air currents after about 1/2 hour of
acclimation, though the inside of the tube is coated with a 1/8" sheet
cork.