Telescope mirror questions?

[Tareq A]

I was wondering about a few questions regarding telescope mirrors, I will post them, and if anyone would like to answer any, please do, as I am planning to grind my own mirror in the future

1) What happens if you make an 8" f/2, would that work? I was wondering why most telescopes have a focal ratio of f/6-10, wouldent it theoriticly work, since its a parabolic mirror?

2) Where can I obtain an 8" mirror blank within reasonable prise? 100$ seems a bit hefty for an ungrinded mirror

3) How long would it take to grind such a mirror, with no power tools, only your hands and the grits

4) would the night sky in the subers of a city be clear enough for viewing objects such as Saturn?

These are all the questions that I can currently think of, thanks in advance!

[campbelp2002]

1) Yes you can but it has problems. Off center images will be distorted, because a paraboloid only brings light to a perfect focus along its axis of symmetry. There are many other problems, like the giant size needed for the diagonal in a Newtonian design and focusing has to be more exact.

2) $100 is the going price it seems. It was $25 back in the 1970s, when Gas was $0.30 /gal. This is one reason telescope making is no longer popular. Commercial telescopes are so cheap now.

3) A few hundred hours labor. A few weeks or months time, depending on how long you work each day.

4) Yes. Planets are bright enough to see in any city sky. Galaxies and other dim objects need a dark country sky.

[campbelp2002]

1) Yes you can but it has problems. Off center images will be distorted, because a paraboloid only brings light to a perfect focus along its axis of symmetry. There are many other problems, like the giant size needed for the diagonal in a Newtonian design and focusing has to be more exact.

2) $100 is the going price it seems. It was $25 back in the 1970s, when Gas was $0.30 /gal. This is one reason telescope making is no longer popular. Commercial telescopes are so cheap now.

3) A few hundred hours labor. A few weeks or months time, depending on how long you work each day.

4) Yes. Planets are bright enough to see in any city sky. Galaxies and other dim objects need a dark country sky.