In 1753 he invented the heliometer, and four years later discovered that an achromatic lens could be made by using two different types of glass, crown glass and flint glass. Although the principle had been discovered earlier, it was not widely known, and Dollond received the credit for his independent invention. In 1765 his eldest son, Peter Dollond (1730–1820), developed the achromatic triplet lens by placing convex lenses of crown glass either side of a biconcave lens of flint glass.