The Great Paris Exposition Telescope, 1900... largest refracting telescope

In 1900, the Great Paris Exhibition Telescope. In 1900, the Great Paris Exhibition Telescope was unveiled at that year's Paris Universal Exhibition. It had interchangeable lenses for visual and photographic uses, but its main primary lens diameter was 49.2 inches with a 187 foot focal length. The project was headed by François Deloncle (1856–1922) and took 8 years to build. It was made primarily for exhibition purposes and was so heavy, long and awkwardly mounted that pointing the scope was nearly impossible. Soon after the exhibition it was dismantled. All that remains are the lenses, which are still kept at the Paris observatory.

Great Paris Exhibition Telescope of 1900 [Wikipedia]