Looking via google, there are photos of this lens in a mount with aperture.
From the VM:
Xenon f2.0 125mm This certainly was an aerial lens, from WW2, originally for Handkammer HK 12.5/7x9 or Rb 12.5/7x9 mounted camera. This was from the firm of Fritz Voelk of Berlin which was destroyed by bombing in WW2 and seems now forgotten. The lens came on the market postwar in fair numbers and was mounted for miniature cameras. Some were coated, but not on all surfaces on that seen, and this may be repairers work as the latest number seen was not coated. Those seen were engraved as made by Schneider (not ISCO), Goettingen, though the serial numbers are anomalous at No48,04x, 44,92x, 51,81x and 57,283 (uncoated) suggesting that a new series of numbers was being started there. The iris only closes to f11. It is a foreward looking lens, sharp and contrasty and covering nearly 6x9 but not 5x4.