Tessar

The Tessar is a photographic lens design conceived by the German physicist Dr. Paul Rudolph in 1902 while he worked at the Zeiss optical company and patented by Zeiss in Germany; the lens type is usually known as the Zeiss Tessar. Since its introduction, millions of Tessar and Tessar-derived lenses have been manufactured by Zeiss and other manufacturers, and are still produced as excellent intermediate aperture lenses. The Tessar design uses four spherical lens elements in three groups, one positive crown glass element at the front, one negative flint glass element at the center and a negative concave flint glass element cemented with a positive convex crown glass element at the rear. History Beginnings Despite common belief, the Tessar was not developed from the 1893 Cooke triplet design, although it appears the Tessar replaces the single rear element of the Cooke triplet with a cemented achromatic doublet. Instead, the Tessar underwent a parallel evolution from Paul Rudolph's 1890 Anastigmat lens, which had four elements in two cemented groups. Hugh L. Aldis patented the Stigmatic lens line for Dallmeyer in 1895; in one implementation, the front group from the Anastigmat design was modified by adding a narrow air gap, which acted as a positive element and improved zonal correction. Later, Rudolph adopted the same device to modify the Anastigmat design, resulting in the Unar of 1899. In addition, this allowed the photographers to have greater freedom when choosing the lenses. In one implementation, the Unar has four air-spaced elements in four groups, which replaced the two cemented interfaces of the earlier Anastigmat design.