On Thursday, 22 June 2017 06:54:34 UTC+2, StarDust wrote:
On Tuesday, June 20, 2017 at 8:53:47 PM UTC-7, BogeyOne wrote:
StarDust wrote:

How good these Mead/Celestron 8" DOB telescopes for $400 or so?
I'm thinking to get one, getting tired of the goto world!

Can't speak for the 8 inch dobs, but I have a Meade 12.5 inch dob and
an extremely happy with it. But it is heavy. It is not a truss but
rather a solid tube. The primary mirror is excellently figured. I
did replace the focuser.

Muscle DOB, eh?
My friend had an old 11" DOB, cardboard tube , heavy. He liked it for a wile, but after grew his backyard out and had to transported to sights, was complaining all the time about it.
Finally he sold it.

The r² in Pi x r² x L, is heavily against any increase in diameter of typical telescope tube materials.

I looked at all sorts of options for my 10" f/8 and even carbon fiber sandwich gets rather "lumpy." [A technical terms for difficult to lift and move around.]

Solid cardboard, steel and aluminium were all in the 25lbs 'bare' range for a 12"Ø tube 7' long.
With only a little weight saving using CF or Tufnol type Hard Paper tubes.
Very disappointing for those who must carry an OTA outside to observe.

Aluminium truss tubes seem most promising provided plywood is not involved for the rings.

The lightest tube I have ever tried was rolled and laminated birch aircraft plywood. With thin baffles of the same material as a former. The trick is to keep everything as thin as possible because birch ply itself is pretty dense!

Balsa wood cries out to be a filler for a sandwich between ultra-thin plywood for rings or support cells.
Egg-crate laminates have been used for decades in aerospace and doors. The problem is how to use them for a telescope tube. Perhaps as a beam?

Builder's straight edges are wonderfully light aluminium profiles but need discipline in their use to achieve overall lightness. I'm still working on that.

But this is hardly the appropriate place for discussing telescope making...