Jan en Harmanus van Deijl. Een optische werkplaats in de 18e eeuw

Jan and Harmanus van Deijl. An optical workshop in the 18th century The optical workshop of Jan van Deijl (1715-1801) and his son Harmanus (1738-1809) was well known in 18th-century Amsterdam. The Van Deijls made telescopes of very good optical quality and Harmanus claimed they had invented some real improvements which also enabled them to construct achromatic microscopes. Measurement on some extant instruments in the collection of the Utrecht University Museum and on one telescope in a private collection show that these claims were well justified and that the Van Deijls could work within rather narrow mechanical tolerances and make adequate corrections for the variations in optical properties of 18th-century glass.