Zenit cameras by Alexander Schulz

Although written in German, I enjoy this spectacular book a lot. Inside you will find an information about early M39 thread Zenit cameras, including Zenit, Zenit-C, Zenit-3, Kristall (Kristall-2), Zenit-3M, Zenit-E and Zenit-B cameras with prototypes.

Online version of the book: http://www.g-st.ch/privat/kameras/zenitbuchtext.html