The largest refractors

Diameter of the lens (in cm)	Focal length (in m)	Observatory	Site	Date of first observation
102	19,4	Yerkes	Williams bay, Wisconsin, USA	1897
91	17,6	Lick	Mt Hamilton, California, USA	1888
83 and 62	16,2	Paris	Meudon, Hauts de Seine, France	1891
80	12,0	Potsdam	Potsdam, Germany	1899
76	17,9	Côte d'Azur	Nice, Alpes Maritimes, France	1887
76	14,1	Allegheny	Pittsburgh, Pennsylvania, USA	1914 and 1985
71	8,5	Royal Greenwich	Greenwich, Londres, UK	1894
69	10,5	Vienna	Vienna, Autriche	1878
68	21,0	Berlin	Berlin, Treptow, Germany	1896
67	10,9	Johannesburg	Johannesburg, South Africa	1925
67	9,9	Mc Cormick	Mt Jefferson, Charlottesville, Virginia, USA	1883
66	10,8	Mt Stromlo	Mt Stromlo, Australia	1925
66	9,9	U.S. Naval	Washington, D.C., USA	1873
66	6,8	Royal Greenwich	Greenwich, Londres, UK	1897
66	9,9	Pulkovo	Saint-Petersburg, Russia	1912

Below, Europe at night showing the light pollution.
Finding a favorable site for astronomical observation is now difficult in Europe.
The existing telescopes must observe only bright objects.

Credit : DR