Thanks
Its a standard Canon EF lens, F1.8. I did my first shot at F1.8 and there was some coma at the edges but not as much as Id get with no filter, I think that the filtered light helps cut down the coma. Manual focus was near impossible as the filter made starts too faint, instead it was by trial and error, taking a few short exposures @f1.8, moving the focus very slightly each time till stars sharp. I then stopped down to F4.
Scott