Carl,
Your confusing all terrestrial telescopes with Galileo's. The
Galilean telescope of course uses a negative lens for its eyepiece. If first
order optics, i.e. simple geometrical optics were the only consideration
these would be the only kind of telescope you would find because they are
very cheap to make. Unfortunately as Galileo knew, his design suffers from a
rather limited field of view that gets worse as the magnification gets
greater. Galileo most powerful telescope had a magnification of about 30
where as his most commonly used instrument magnified seven times. This is
the same as common binoculars used today, but these are made using positive
lens optics and a prism erecting system.
The problem with Galileo's telescope is its field of view. The
higher the magnification the smaller the field of view. It appears that your
looking the wrong way down a mailing tube. Positive lens telescopes don't
suffer from this limitation, which is why it is used not only for
astronomical telescopes but terrestrial ones as well.
I hope this helps.
Gary
Gary Karshner
St. Mary's University
San Antonio, Texas
KARSHNER@STMARYTX.EDU