The development of building a telescope was greatly aided by the construction of the achromatic lens.

The Achromatic Refractor
In 1733, the achromatic lens was invented by Chester Moore Hall, an English barrister. This was accomplished by combining a convex crown and a concave flint lens in such a way that their focal lengths were inversely proportional to their dispersions.

Although a number of telescopes were made according to Hall’s instructions, the benefits of the achromatic lens do not appear to have been made available to the public until John Dollond invented it independently in 1758, and patented it. Dollond’s efforts led to a demand for clearer glasses of more varied densities and of less equal dispersions, needed to improve achromatism, and chemists pursued experiments in learning how to control the refractive indices of melts, and in the pouring of large disks of limpid, homogeneous glass. more…