<P> The earliest known telescope appeared in 1608 in the Netherlands when an eyeglass maker named Hans Lippershey tried to obtain a patent on one . Although Lippershey did not receive his patent, news of the new invention soon spread across Europe . The design of these early refracting telescopes consisted of a convex objective lens and a concave eyepiece . Galileo improved on this design the following year and applied it to astronomy . In 1611, Johannes Kepler described how a far more useful telescope could be made with a convex objective lens and a convex eyepiece lens and by 1655 astronomers such as Christiaan Huygens were building powerful but unwieldy Keplerian telescopes with compound eyepieces . </P> <P> Isaac Newton is credited with building the first reflector in 1668 with a design that incorporated a small flat diagonal mirror to reflect the light to an eyepiece mounted on the side of the telescope . Laurent Cassegrain in 1672 described the design of a reflector with a small convex secondary mirror to reflect light through a central hole in the main mirror . </P>

When was the oldest of the telescopes built