That lens comes with 2 filter holders, one for the 39mm screw-in, and one for small gelatin filters, which is the one it sounds like you have. You should be able to obtain the other holder, perhaps from B&H.
- 300mm f4 AF/ED filter dilemma? George Treible
- Re: 300mm f4 AF/ED filter dilemma? Ron Goodman
- Re: 300mm f4 AF/ED filter dilemma? larry angier