50mm f1.4 id an extended Ultron design - which Zeiss has labeled as a “Planar” since the mid 60s - important because thats when Zeiss and Pentax had the cooperation research agreement that ultimately yielded the K mount. The Takumar, Rollei Zeiss Planar and contax Zeiss planar 1.4s are all extended Ultrons- the 105 is a biotar - arguably the biotar is a better design than the standard planar - but the extended Ultron type planars all had the highest test MTF/LPM in the 70s and 80s.