The Tube
Making a 4.25 Inch Dobsonian
Reflector Telescope
For an inexpensive telescope,
Sonotubes (a brand name) are usually used.
These are extremely sturdy cardboard tubes made as cement forms. People use them for all sorts of other
applications including telescope tubes.
Once painted, they can look appealing while retaining a telltale spiral
that lets anyone looking know that the scope is home built.
A few minor points. Don't cut your tube until you know the
focal length of your mirror. The tube
should be at least as long as the focal length, and them maybe a few inches to
spare. Expect cutting a tube by hand
to be quite a chore. An electric saw
is a good idea. Before painting the
tube, make sure you've removed the plastic coating it comes shipped with. Painting a tube can be difficult. The cardboard tends to soak up anything
liquid. I've tried Varathaning the
tube first with limited success. The best
results were spray painting the outside with a dark glossy color. Almost 3 coats were needed. For the inside, use flat paint to minimize
reflections.
Lastly, do not cut the hole for the
focuser until you have installed the secondary. Put a plastic bag around the secondary to protect it from dust.