The ZK Zorki (ЗК Зоркий) 5cm f/2 was one of the forerunners of the Jupiter-8. ЗК stands for Sonnar Krasnogorsk. The early models were assembled by KMZ, not yet in Arsenal. Also, KMZ assembled the early versions partially or completely from materials they sacked from the Carl Zeiss factories of Jena and Dresden. I can't say which parts of my particular lens are "Made in Germany", but the picture quality of this lens is quite good and is a bit better then the 1950s Arsenal-made Jupiter-8 lenses that I own (read my blog entry: the Arsenal Gang).

Princelle lists this lens as K520; SovietCams as PT3525

Aperture range: f/2-f/22
Minimum focussing distance: 0.9m
Aperture blades: 9

The serial indicates that the lens was made in 1950. It also bears the П-mark, indicating that the lens was coated.

You can take a look at its dedicated gallery on my website

An example of this lens:

NEX-5 + ZK Zorki 5cm f/2 (ISO200, f/11, 1/250s)

Some Boring Lens Tests (FLT.II):

flare at f/22

Out-of-focus rendering (pictures taken at minimum focussing distance):

f-stops: f/2 - f/2.8 - f/4 - f/5.6 - f/8 - f/11 - f/16 - f/22

The ARG-file I use with exiftool: zkzorki_5cmf2kiev_5002234.txt

-n
-ex
-XMP:SerialNumber=5002234 Π
-EXIF:LensModel=ЗК ЗОРКИЙ 5cm f/2 Π (Киев)
-EXIF:maxaperturevalue=2
-EXIF:focallength=50
-EXIF:focallengthin35mmformat=50
-EXIF:fnumber=2

This works for LR4 and NEX-5 RAW-files. The code will show up as "ЗК ЗОРКИЙ 5cm f/2 Π (Киев)" in LR4.