In the history of the telescope, almost no attention has been given to the development of the achromatic binocular telescope: a scientific instrument that emerged in 1770. New archival evidence suggests that this instrument owes much to the efforts of the Dutch scholar and philosopher Frans Hemsterhuis (1721–1790). In the present literature Hemsterhuis is best known as the most important Dutch philosopher of the eighteenth century, well known for his theories on aesthetics. But he had also a profound interest in optics. According to Hemsterhuis’s correspondence it was his aim to improve the resolution of the telescope. Stimulated by the invention of the achromatic telescope in 1758, Hemsterhuis examined and tested most of the early achromatic telescopes constructed by the Dutch opticians Jan van Deijl and his son Harmanus. After a failed attempt to improve a large (12-foot) reflecting telescope produced by the Franeker telescope maker Jan van der Bildt, Hemsterhuis designed an achromatic binocular telescope in 1770. In the following decade a number of these binoculars were ordered from the well-known London firm of Peter Dollond, some of which were distributed among Hemsterhuis’s friends. His instruments were admired by several visiting scholars, such as Giò Francesco Fromond (1771), Jacob Jonas Bjornstahl (1773), Jérôme de Lalande (1774) and Marsilio Landriani (1788). Hemsterhuis’s sudden death in 1790 however forestalled his intended publication on this topic, with the result that, until now, Hemsterhuis’s efforts in this field were largely forgotten.