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 My telescope's main tube is made out of heating duct pipe. The top and bottom of the scope are cooking pots that were cut up appropriately. One design aspect that I modified (a few times) is the mirror mounting cell. The mirror is over an inch thick, so you'd think the thing would never warp. Still, it only takes a very small deformation of the mirror to change the image. The idea is to support the mirror as evenly as you can. You need to keep the mirror from falling out of the scope, but you don't want to exert any force on the mirror from the clips, or otherwise hold it down.
 The mount needs to have adjustments so that you can fine tune the angle at which the mirror is pointed. This angle must be exactly in-line with the tube and secondary mirror, and there must be adequate air flow around it to equalize the temperature in the scope. The traditional telescope design sits the mirror on a platform, but also includes something to catch the mirror in case it falls forward. My platform has three screws in a triangle (with springs) so that you can adjust the angle. This layout also has holes or pathways for air to flow around. I made my platform out of a hard plastic; well, actually, I ended up using plastic cutting boards. Do you see a kitchen theme here?
 The spider is the part of the telescope that suspends the secondary mirror in the middle of the tube. I made mine out of metal straps, a bolt, and some PVC parts. I opted to glue the secondary mirror to the mount. I also made the secondary mount adjustable in the same way as the primary mirror. So, I have two washers; one has three holes which I tapped with screws to make my adjustments. To connect the spider to the tube, I welded nuts onto the ends of the straps. I then drilled holes into the metal pot at the top and connected the spider with long screws. This allowed me to carefully center the spider and keep it tight. For the focus adjustment, I bought a used camera zoom lens, removed its guts, put in a pipe to fit the eye pieces
The next important part is the mount on which the the scope sits so that you can point it and keep it steady.
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Re: Making a telescope Part 2
