If like me you hate the caps and the hoods (even if I must say that with that is the most beautiful goal that I've ever owned) and having seen the leica filter holder for 18 is taken a facial paresi (a pan of 77mm) I propose this solution. I went by trial and went down from 77 up to 62! It was enough to couple a 62-58 step down filter and apply it to the male thread of the lens, then screw down the filter (slim) you want. Then to avoid throwing a rubber washer made out of an inner tube. In this way you also avoid unscrewing and protecting it from dust. I will try again to make sure that there is not even a hint of vignetting, but from the first tests it seems ok. We are ready for the dunes of Morocco
have a nice day!