The achromatic lens, which greatly reduced color aberrations in objective lenses and allowed for shorter and more functional telescopes, John Dollond learned of Hall's invention[2][3] and began producing telescopes using it in commercial quantities, starting in 1758.
Important developments in reflecting telescopes were John Hadley's production of larger paraboloidal mirrors in 1721; the process of silvering glass mirrors introduced by Léon Foucault in 1857;[4] and the adoption of long lasting aluminized coatings on reflector mirrors in 1932.[5] Almost all of the large optical research telescopes used today are reflectors.
The era of radio telescopes (along with radio astronomy) was born with Karl Guthe Jansky's serendipitous discovery of an astronomical radio source in 1931. Many types of telescopes were developed in the 20th century for a wide range of wavelengths from radio to gamma-rays.