The first astronomical telescopes contained only simple lenses. For the
discoveries made by Galileo, such simple instruments, with their low powers,
were adequate. But soon the race for magnification was on. The problem was
that along with the fine details, the objective's aberrations were also
magnified. Chromatic and spherical aberrations were the main villains.
Early telescope makers soon discovered that both problems could be controlled
by using very large focal ratios. However, the monster telescopes which
developed in the mid-17th Century were extremely unwieldy.
Christian Huygens was the first to discard the long wooden tubes of earlier
instruments. His first "aerial" telescope was 2 inches in aperture, with a
focal length of 123 feet! The objective and eyepiece assemblies were
connected by a long string. The eyepiece was held in the hand, while the
elbows rested on a waist-high bipod.
Huygens' first discovery was astronomical seeing. He found that atmospheric
currents hindered the telescope's ability to image small details. Later, his
drawings of Mars provided the basis for our accurate determination of that
planet's rotation period.