Newton’s telescope used curved mirrors instead of lenses to focus light. Telescopes that
use mirrors are calledreflecting telescopes,orreflectors(Figure23.6). The mirrors in
a reflecting telescope are much lighter than the heavy glass lenses in a refractor. This is
significant, because thick glass lenses in a telescope mean that the whole telescope must be
much stronger to support the heavy glass. In addition, it’s much easier to precisely make
mirrors than to precisely make glass lenses. For that reason, reflectors can be made larger
than refractors. Larger telescopes can collect more light, which means they can study dim-
mer or more distant objects. The largest optical telescopes in the world today are reflectors,
like the one inFigure23.7.
Figure 23.6: Reflecting telescopes used by amateur astronomers today are similar to the one
designed by Isaac Newton in the 17thcentury. ( 13 )
Many consumer telescopes today use a combination of mirrors and lenses to focus light.
These telescopes are calledcatadioptric telescopes. By using both kinds of elements,