approached Ernst Abbe from the Zeiss works in Jena. Abbe soon appointed Czapski as his assistant – a post he held until 1886 – and involved him in his discussions with the physicist Leonhard Sohncke from the University of Jena. As Abbe's assistant, Czapski maintained a relatively loose connection to Zeiss as a company and continued to accept work from Bamberg, but all that changed in 1886 when he was hired to work full-time at Zeiss, becoming Abbe's most trusted employee with the approval of Carl and Roderich Zeiss). Abbe involved Czapski in his theoretical studies as early as 1885. It was Czapski who went on to publish these studies the following year because Abbe himself had neither the time nor the patience, being too occupied with his development projects. In 1893, after five years of work, Czapski finally completed his contribution to Adolf Winkelmann's Handbuch der Physik (Encyclopedia of physics) entitled Theorie der optischen Instrumente nach Abbe (Theory of optical instruments according to Abbe). The 300-page work was issued that very same year as a separate publication from volume II of the encyclopedia and was hailed as a key work in the field of technical optics. Working with Abbe and Otto Schott in Jena and with Leopold Dippel in Darmstadt, Czapski was involved in the design and fabrication of new microscope optical systems from the moment he started work in Jena. He subsequently worked on the technical implementation of a binocular microscope based on ideas put forward by the American biologist Horatio S. Greenough. As the company expanded, so too did its range of products: Zeiss started producing photographic objectives in 1890, optical measuring instruments in 1892/93, prism binoculars in 1893/94 (a development based on significant input from Czapski), astronomical instruments in 1897 and image measuring devices in 1901. Czapski steadily took on more and more responsibility as Zeiss increased its product portfolio and workforce and as its fame spread far beyond the borders of Germany. In 1891 he became one of the company's three managing directors. Establishment of the Carl-Zeiss-Stiftung Founded in 1889 by Abbe, the Carl-Zeiss-Stiftung (Carl Zeiss Foundation) took the entire Zeiss company and half of the Schott company under its wing in 1891. Czapski was subsequently appointed as an authorized representative of the Foundation. Working closely with Abbe and a foundation inspector from the Grand-Ducal Saxon State Ministry in Weimar (initially Karl Rothe and from