Neither Newton nor Galileo invented the telescope. It was
developed independently by various dutch optics makers (Lippershey
submitted the first patent). Galileo's first telescope was
dutch-made, and he made useful improvements to the initial
retractor design. Newton did invent the reflecting telescope (the
particular design is now called a Newtonian Telescope). Further
improvements to the reflector design were made by Cassegrain and
others made improvements to the manufacturing process, greatly
improving the mirror quality.
A refracting telescope uses a lens as the main objective, while
a reflecting telescope uses a mirror. The objective is the
component that focuses the light. Reflector telescopes are the most
common nowadays, as they do not suffer from chromatic aberration
(light splitting due to refraction) and can be built in very large
diameters.
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Galileo improved the refracting telescope, but Newton invented
the reflecting
telescope.
