Reflectors (Newtonians)

As telescopic astronomy developed it became obvious the larger and larger lens were desired.  As the diameter of a telescopes lens increases, its ability to collect light increases in squares.  The problem is that as these lens get larger their cost also goes up dramatically.  This was solved by Isaac Newton (1643-1727) who invented a telescope using a concave mirror instead of clear convex lens.  Since concave mirrors are far easier to manufacture than convex lens the price of these telescope are far cheap per aperture than a refractor scope.

In 1670, Isaac Newton invented the Reflector telescope (sometimes referred to as a Newtonian Scope) for which he first became famous. (That “gravity stuff” came much later in life.)

A Newtonian Reflector is characterized by a concave mirror at the bottom of a telescope tube.  The mirror bounces the light back up the tube to a secondary mirror which bend the light 90 degrees out to the focuser and eyepiece.  Because the image orientation is not easily controlled these scopes, while making excellent astronomy telescopes, are not as easy to use for daytime, terrestrial viewing.