The materials I've got...

I have 11 lengths of 3mm hardboard, 75mm wide with a 45deg bevel down one side. The nice man at B&Q tried his best with a second sheet and just one came out wonky. From a 9mm laminate/mdf sheet about 2'x2', I have cut 18 ribs, 1/3 of a round each. These provide an internal aperture somewhere between 240 and 245mm. These all have a 45deg bevel on the inside diameter to about 7mm - not quite knife edge, but I needed some meat to run on the router bit bearing.

The original plan...

I was going to cut to length at 1.7m and fit 6 sets of ribs along the length. This was my 'least cost' option - one sheet of hardboard, a tube or two of high strength grip adhesive, a few rolls of masking tape and some spare paint/varnish. However, in mocking up a round using 5 inch 'test pieces' of hardboard cut from one end of the full lengths, I see a rather nice secondary/focuser stage for a truss newt.

The new plan...

I can save myself a lot of handling of long, floppy lengths of hardboard by going for a truss design. I'll save wood too, so I can probably get both primary and secondary tube stages for the binoscope made out of the materials I've got cut and prepared already - perhaps just a few more ribs! The extra money spent now in making this scope (or these scopes!) lightweight and portable will surely pay off in the end.

When I run the bead of adhesive between the outer sections and then fold them to 150 degrees, I'll wet-finger the bead down into the joint and then lay on top a length of bamboo skewer (£1 for >100), cut to fit between the two baffles, and then run another bead of adhesive over them once the first has cured. It'll add weight, not a lot, and should increase the strength of these edge-edge joints. The inside surface of the hardboard is already "waffly" - my "poor man's flock". Inside will be sealed and painted matt black. Outside is still a few coats of exterior varnish, for now.

Now to source a dozen truss rods - budget £20 or so. The focal length is >1.5m, so a Serrurier truss might let me use slightly shorter lengths, like floor brush handle tubing or something.

Had I seen this page (http://astronomyasyl...ultralight.html) before starting all this, I would have easily put the cost of a sheet of 18mm ply to this build (£28) - but the hardboard only cost about £5, which I've already spent so I'll continue with that, but go 'truss' with them. I may take some inspiration from here (http://www.rfroyce.c...russ_tube_newt/).