the question is ungrammatical. Restate it.
lenses
A refractor
Galileo
Most telescopes use refractor lenses. Sometime a telescope will use reflector lenses.
The Newtonian Telescope.
One major problem with the refractor telescope used by Galileo was sagging lens.
He invented the reflecting telescope. Galileo was the first to use the telescope for studies of the heavens.
The YOSCO - much better
The Emerson 50x is 12mm and the 100x is 6mm.
simplest possible telescope
refractor
a refractor or a reflector are two types of telescope.