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.