The Development of Telescope Optics in the Middle of the Seventeenth Century

The author performed optical tests on four telescopes dating from the first half of the seventeenth century and on four objective lenses made by the Italian optician Giuseppe Campani. These tests consisted of the method of Ronchi and of the highly sensitive method of Foucault on an optical bench. The two incomplete surviving telescopes in Skokloster made by Wiesel have been reconstructed and compared with a telescope made by Divini and a telescope made by Campani. The contributions of Schyrl de Rheita and Johannes Wiesel to the development of the telescope, and the influence of their new methods upon the opticians of the second half of the seventeenth century, especially Giuseppe Campani, are discussed.