a telescope can be used to observe the sun safely by removing most of the light that is coming from the sun. Many amateur telescopes can be fitted with a solar filter which removes most of the light before a human or a camera would look at it. For professional solar telescopes, the same kind of thing happens, in part because we are often trying to study a small part of the sun at very high resolution, or a very small piece of the solar spectrum (A very tiny piece of what you would see having put some sunlight through a glass prism, for example). In the case of what I do, in addition, we look at the polarization signature of the light coming from the sun, using instruments that are in some ways similar to very high-tech polarizing sunglasses. In that way we break apart the solar spectrum even further, and believe it or not for professional solar telescopesthe observations become "photon starved". in general, we do not look what our eyes through the telescopes, but to use a camera very similar to the digital camera you may have, to record what we need from the solar telescope.

that being said, I do have to say do not look at the sun with your eyes or even through a piece of plastic that looks dark enough, unless you are informed by an adult that it is safe. the best way to observe the sun completely safely is using a pinhole protection system. there is a good explanation of how to make one at http://www.exploratorium.edu/eclipse/how.html and http://www.spaceweather.c...ts/doityourself.html