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I watch the Deep Sky Videos channel on Youtube, and a guy there has a a telescope with a carbon tube, looks quite cool. The bits you mentioned can definitely be made of carbon. The only real benefit will be weight. They wont be stronger, but strong enough. You could make them thinner too. 3 layers of 200gsm prepreg will give you 0.5mm, but you might get away with 2 layers (.3mm)
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Question from a beginner. But first let me explain the situation. Consider a Newtonian telescope, as shown in an image here:  At the top of the tube, you can see inside 4 straight elements holding a central component. That's the secondary mirror, inclined at 45 deg, kept in place by the so-called "spider"; the 4 elements are the spider vanes. Here's a detail view from a different scope:  And here's another mirror holder and spider (with nice tapered vanes), disassembled:  The spider's function is to hold the secondary mirror in place as rigidly as possible. As the scope is moved from one place to another, bumping it into objects tends to move the secondary mirror a little bit, which then requires readjustments. A good spider can keep a mirror aligned for a long time. This is achieved via tension. The end of each vane is anchored to the tube via screws, which are then tightened as much as the tube would allow without crushing. This is not an exact science, but usually the limiting factor is the strength of the tube. You tighten the spider until the tube shows signs of stress, then back off a bit; if the vanes sound like violin strings when plucked or poked at, then they are probably tight enough. So you want the vanes to be strong. On the other hand, the vanes intersect the path of light, and therefore create artifacts in the image. The thicker the vanes, the stronger the artifacts. To keep artifacts down, you want thin vanes. They are usually made of steel, around 0.75 mm for most scopes, or even 1.25 mm for very large scopes. To me, this contradiction between high tension on one hand, and thin vanes on the other, sounds like exactly what CF composites are made for. Is it possible to make thinner but stronger vanes out of CF? How thin could I, an amateur, make a CF sheet that would still be reasonably strong? Is it possible to make, say, a 0.5 mm vane that would be stronger than the steel equivalent? What would be the challenges of attaching a CF vane to the fastener at the outer end, and to the central hub at the inner end? BTW - the attachment points at each end of the vane need not be very thin, since those parts do not intersect the incoming light. Finally, the vanes need to be flat black (non-reflective) in color. Steel vanes are usually painted. I assume a piece of fine sandpaper would take the shine off a CF sheet, right?
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