This is part IV of a series of what glass you will need. Each part will discuss a certain lens type and its applications.
Medium primes are lenses in the range of 85-200mm (in FX terms) or 58-135mm in DX.
This segment is very interesting as you find here lenses with with the lowset f-number/focal-length (if we neglect long tele lenses). In other words: These lenses allow for extreme subject separation.