Hey Alex the 18mm proved to be suited for the job and the result was great even with the high ISO.
Have to agree the 50mm didn't deliver and the noise is pretty bad, I have found that the stars will distortion at the edges because putting a 50mm lens on the Infinity Line on the barrel of the Lens is not really Infinity.
I, (and you probably are aware of this,) first put the Lens on Auto point it at a distant street light or similar and get it focused then switch to manual and take the shots at any length you want.
Just my two cents worth.
Good effort on the first one though.
Leon