Contax Planar 2/45

After seeing all the great picutes taken with this lens on NEX cameras, I finally broke down and bought one, dispite the less than ideal focusing system. It arrived today, and looks great, with one exception.

When the lens is wide open the index says that it is at f:8. Then it goes to 11 and 16 with 4 more clicks past that into unmarked territory. The index never does line up with f5.6 - 4 - 2.8 - or 2. Am I doing something wrong? Does the lense need to be on an adapter before it registers properly? Or does it need a trip to the repair shop?

Thanks