OO> Our society's 20" f/4 has a multi (12?) section wooden tube, mounted OO> on a massive fork mount. Being f/4, it is EXTREMELY sensitive to
Bratislav,
If I understand you correctly, you are speaking of a completely enclosed wooden tube? Hmmm, I've built two such tubes for 8" scopes and have had no problems. Possibly larger dimensions with wood would tend to flex more causing the allignment errors. Most of the larger instruments that I've seen constructed of wood only have the mirror box and base of wood. The tube itself is normally joined with aluminum tubes (mirror box up to the cage), such as with the Obsession type designs.
My current tube is an 8" square box constructed of 22mm plywood with the same 22mm material used in making 7 baffles/bulkheads. The tube when assembled is 7' long to accomodate the 75.6" fl mirror. The tube is built in two sections, each being 3' long. I've never experienced colimation problems while in use, however, I do have to colimate after transporting the tube or immediately after rejoining the two halfs.
Note that you pointed out the possible exageration of the problem due to the differences in focal length (yours f/4 and mine f/9 <g>). Good point.
Mike
* RM 1.3 * I'd love to, but the President said he might drop in.