Wikipedia
The Tessar is a famous photographic lens design conceived by the German physicist 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.
A Tessar comprises four elements in three groups, one positive crown glass element at the front, one negative flint glass element at the center and a negative plano-concave flint glass element cemented with a positive convex crown glass element at the rear.
Despite common belief, the Tessar was not developed from the 1893 Cooke triplet design by replacing the rear element with a cemented achromatic doublet. In fact, Paul Rudolph designed the Anastigmat with two cemented doublets in 1890. In 1899, he separated the doublets in the Anastigmat to produce the four-element, four-group Unar lens. In 1902, he realized that reversing the two rear elements of the Unar and returning to a cemented doublet would improve performance; he named the result "Tessar", from the Greek word τέσσερα (téssera, four) to indicate a four-element design.
Early Tessar designs by Paul Rudolph allowed a maximum aperture of f/6.3. Later development allowed an aperture of f/4.5 by 1917. In 1930, Ernst Wanderslab and Willy Merté of Zeiss developed Tessar lenses with apertures of f/3.5 and f/2.8.