Zeiss Planar

Rudolph's original was a six-element symmetrical double Gauss lens design.

While very sharp, early versions of 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.

These lenses used the Zeiss T coating system, which had been invented by Olexander Smakula in 1935.

[1] They performed very well as normal and medium-long focus lenses for small and medium format cameras.