The darker blotch, central to the shot,is on the inside surface of the lens.It resembles a muddy fingerprint.It appears that to remove said blotch,I may have to have the lens professionally cleaned and rebuilt.NB :Said blotch has now,July 2018,BEEN REMOVED/CLEANED,by Fuji.Exactly how,and exactly what it was has not been imparted to me by Fuji(uk).I sent the lens to them ,they did the necessary and returned it to me.It's now as good as new.(July 2018).