Planar.

The Zeiss Planar is a photographic lens designed by Paul Rudolph at Carl Zeiss in 1896. Rudolph's original was a six-element symmetrical design.
While very sharp, the lens suffered from flare due to its many air-to-glass surfaces. Before the introduction of lens coating technology the four-element Tessar, with slightly inferior image quality, was preferred due to its better contrast. In the 1950s, when effective anti-reflective lens coatings became available, coated Planars were produced with much-improved flare. These lenses used the Zeiss T* coating system, which had been invented in 1935.[1] They performed very well as normal and medium-long focus lenses for small and medium format cameras.(Source Camerapedia)