One of my best lenses is the CarlZeiss Sonnar 135mm, the version I have is the zebra, is not the last or the modern version but is one of the best lenses made, (most sonnar are), their history comes from 1932 by Ludwig Jakob Bertele, he calculated and created the lenses configuration so the aperture could get to f2.0 that was remarkable at that time.
The name Sonnar in german it means sun, the first appear at the begining of the 1930 for the camera Zeiss Ikon, having great success for sharpness and contrast, and going apertures till f1.5, now is quite rare to find those lenses now and they are collector items, very expensive.
Bertele builded in 1936 the Sonnar 180mm f2.8 ( 7 elements 3 groups) for the Olympic Games of the nazi Germany, since then the optical formula has was used for the next years in different brands like the russian Jupiters, Canon 50mm f1.5, Nikkor 8.5cm f/1.5 including the last lenses for Sony a7, Carl Zeiss Sonnar T* FE 55mm F1.8
The Sonnar formula was one of the most copied lenses, because at the end of second world war the factory in Jena given to the soviets, they moved to inside Russia and produced the Jupiter lenses that are great, also the other part of the factory of Zeiss was held by US, both factories produced the same lenses till end of the 70’s for Pentax, Exakta and Contact, both are great lenses form Carl Zeiss or aus Jena and have similar quality, mine is produced in Jena.
One of the characteristic of the sonnar is the beautiful bokeh or out of focus that is soft and creamy, also gives separate easy the subject form the background creating the 3D effect.
Even at f3.5 is sharp but has some chromatic aberrations, stepped down things are much better.Is a great lens for portraits because the 135mm focal lenght.
To finalize this is a great lens if you like to manual focus and have the film experience, if you find some in ebay or any store I recommend to try, I can’t say is cheap, vintage glasses are getting more expensive lately, specially now with the mirror-less cameras that can use practically any lens mount. This is sonnar is always in my bag.