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Re: Building A Telescopes Questions

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Posted by Robert May on July 8, 1998 10:48:42 UTC

: I have many ?'s

: 1-What does f/6 for example mean and in what units are they measured. F ratio is measured by the focal length over the primary diameter. It indicates how "fast" the system is. : 2-What do you reccomend size wise for seeing lots of deep space object. Mirror-satigga and focal length and secondary mirror size. Depends upon what your finances are. The larger, the more you can see. If you have the money, a mirror about 30" or so is as big as it appears that you can go and get good images. Larger scopes that I have seen all seem to have something wrong with them that prevents them from being good instruments and as I don't own them or have a long term access to them, I can't tell exactly what is wrong. The bottom end is that I haven't seen anything larger perform well. Satigga (I think that you mean sagitta) is a function of focal length and size of the mirror so you basically said two things at once and the secondary mirror size depends upon what you are doing. I suggest that you look for pages of telescopes and find out what they are doing. There are lots of those pages. Just search.

: 3-How do you grind the primary mirror. Depends upon the size. smaller mirrors (under 12") are easily ground by hand and larger ones it usually makes sense to make a grinding machine for the work as the push needed will quickly tire even Mr. Atlas and it gets to a point where it is impossible. : 4-Can you make homade eyepieces or should you by them. Buy the EP's. Modern EP's have 4 or more pieces of glass in them and the recipies for them are difficult for the beginner. : 5-Does the secondary mirror size matter. Yep. : 6-How long should the tube be. Long enough to hold the optics design at a minimum. The diameter is almost more important as that is one of the things that determines the field of view of the instrument. Also don't forget baffling the tube. It is important for good images and a large field of view.

Have Fun and Keep Looking Up!!!

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