Emil Busch 4.9/21 cm Nicola-Perscheid lens - very rare! small version

Emil Busch 4.9/21 cm Nicola-Perscheid lens very rare! Small compact Emil Busch Nicola-Perscheid 21 cm (210 mm) lens for 4.9 with very clean glass! One of the rarest and best portrait lenses of the 20th century!