I just bought a 1940's German rangefinder, it's a FUTURA S made by Futura Freiburg BR. and the lens is a FRILON f 1.5 50mm. Can't find much about it on the net. It comes without the instruction book. It's pretty straight forward except the following: Shutter speed are B, 1, 2, 5, 10, 25, 50, 100, 250 & 500. Works at all speeds (I don't have facilities to check speeds but they look about right), but, if shutter is cocked (film advanced) while b through to 250 are sellected, you can't sellect 500. After firing the shutter you can then select 500 and advance film (advance wheel appears to offer slightly more resistance than with the lower speeds). After advancing with 500 selected, you can go down the range but can't go back to 500. Does anyone know if this is correct of could it be that the shutter is faulty?