by dgolds3 » Tue Feb 23, 2010 6:10 pm
Hi Orca;
I've built a 6" f5 newtonian telescope from a mirror that I ground. It's a lot of work to grind even a small mirror, it took me a couple of months. For a "light bucket" be prepared to spend a lot more time. A long focal length mirror, f10 and above, you can leave spherical which is the easiest to grind, but then you have the tube, mounting, and space issues to deal with. An RFT, rich field telescope, avoids a lot of these but is harder to grind as you have to match the parabolic figure more precisely. A RFT inherently has lower magnification, but a wider field of view. This is superb for extended objects such as nebulae and galaxies. What do you want to look at? Planets and double stars are seen best with a long focal length instrument, as noted galaxies and nebulae a RFT. Truss designs work well for a RFT, for a long focal length instrument it would cost a lot to get the required rigidity.
My only beef about Dobs is their lack of drive. It gets frustrating to have to "jiggle" the scope every few seconds to keep the image centered. (Although Galileo would have been delighted to have one of our modern Dobs!) If you want to build a scope, go for it. You'll learn a lot about optics, and there's nothing like looking at the Orion nebula or M32 through something you built from hand. But, you really aren't going to save any money. There's the cost of the tubing, mount, drive, eyepieces, finderscope, etc... that are included in commercial scopes. A good 10 inch newtonian will cost about a grand, half to double that for a catadioptric system. Good luck, clear skies, and happy viewing! Don.
Hi Orca;
I've built a 6" f5 newtonian telescope from a mirror that I ground. It's a lot of work to grind even a small mirror, it took me a couple of months. For a "light bucket" be prepared to spend a lot more time. A long focal length mirror, f10 and above, you can leave spherical which is the easiest to grind, but then you have the tube, mounting, and space issues to deal with. An RFT, rich field telescope, avoids a lot of these but is harder to grind as you have to match the parabolic figure more precisely. A RFT inherently has lower magnification, but a wider field of view. This is superb for extended objects such as nebulae and galaxies. What do you want to look at? Planets and double stars are seen best with a long focal length instrument, as noted galaxies and nebulae a RFT. Truss designs work well for a RFT, for a long focal length instrument it would cost a lot to get the required rigidity.
My only beef about Dobs is their lack of drive. It gets frustrating to have to "jiggle" the scope every few seconds to keep the image centered. (Although Galileo would have been delighted to have one of our modern Dobs!) If you want to build a scope, go for it. You'll learn a lot about optics, and there's nothing like looking at the Orion nebula or M32 through something you built from hand. But, you really aren't going to save any money. There's the cost of the tubing, mount, drive, eyepieces, finderscope, etc... that are included in commercial scopes. A good 10 inch newtonian will cost about a grand, half to double that for a catadioptric system. Good luck, clear skies, and happy viewing! Don.