Compare the size of vintage 50mm lenses. The Zeiss Sonnar 5cm F1.5, Canon 50/1.5, Nikkor 5cm F1.4, all small and compact lenses. These are 7 elements in 3 groups. The Leitz Xenon 50/1.5, Summarit, 1950s 50/1.5 Nokton, are much larger lenses. They are 7 elements in 5 groups.The configuration of the optics has a lot to do with things. Sonnars transmit more light and have higher contrast. The Planar formula lenses have better correction for distortion.
The Summitar is a much larger lens than the Summar, both are 5cm f2 lenses. The front element of the Summitar is big enough for an F1.6 lens (Morgan and Lester, "Leica Manual"), designed to improve problems with vignetting in the Summar.
The Summitar is a much larger lens than the Summar, both are 5cm f2 lenses. The front element of the Summitar is big enough for an F1.6 lens (Morgan and Lester, "Leica Manual"), designed to improve problems with vignetting in the Summar.