I believe it's the same fitting as Rollei Bayonet I, which means there's an enormous range of filters out there. And there are add-on tele and wide adapting lenses, varying from Yashica's own, which are pretty cheap and cheerful (i.e. not very good quality), to the outrageously expensive Zeiss Mutars for Rollei, which are of extremely high quality, but if you found any at a knock-down price would be far better sold on at a massive profit. In all honesty, I'm not at all sure it's worth bothering. Close-up lenses can be far more worthwhile, and the Rolleinars I've been alluding to are probably the best.