Great Paris Exhibition Telescope of 1900

The Great Paris Exhibition Telescope of 1900, with an objective lens of 1.25 m in diameter, was the largest refracting telescope ever constructed. It was built as the centerpiece of the Paris Universal Exhibition of 1900. Its construction was instigated in 1892 by François Deloncle , a member of the French Chambre des Députés. Since it was built for exhibit purposes within a large metropolis, and its design made it difficult to aim at astronomical objects, it was not suited for scientific use. When the year-long exposition was over, its builders were unable to sell it. It was ultimately broken up for scrap; the lenses are still stored away at the Paris Observatory.

The telescope had two interchangeable objective lenses 1.25 m in diameter, with a focal length of 57 m . Due to its extremely large size, the telescope was mounted in a fixed horizontal position. Light from astronomical objects was redirected into the optical tube assembly via a Foucault siderostat, a movable plane mirror 2 m in diameter, mounted in a large cast-iron frame at the objective lens end of the telescope. The horizontal steel tube was 60 m long. The telescope’s eyepiece/plate end could be shifted five feet on rails for focusing. With the lowest power of 500×, the field of view was 3 arc minutes.

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