Zeiss is known for both their modern and vintage glass and B-Speeds are certainly part of that discussion.
As Matt Duclos of Duclos lenses said it best:
"The B-Speeds were first introduced in the mid 70’s as some of the fastest prime lenses you could purchase. The set consisted of an 18mm, 25mm, 35mm, 50mm, and 85mm. The B-Speed name comes from the fact that they were originally shipped from the factory in an Arri Bayonet Mount (B-Mount). The lenses had a maximum aperture of T1.4. Note that the front engraving on these classic primes will show a number that is NOT a T-stop rating, but rather an f/stop – hence the “1:1.2, 1:1.3, or 1:1.4” engraving. The /f stop was the theoretical aperture of the lens, factorable, as it were – whereas the T-stop markings on the iris ring were the actual measurable light being passed through the lens, onto the film. Speed aside, one of the most defining features of the B-Speeds is their triangular iris configuration. Despite the lenses have a 9-bladed diaphragm, the shape produced is a unique, unmistakable triangle. Wide-open, the lenses produced beautiful round bokeh, but as soon as you stop down… Triangle bokeh!"