I'm using a Heliopan 3x center filter on a 90mm/f4.5 Nikkor for 5x7. Have any of you used a B&W extra wide filter with this combo? Was there any vignetting? I emailed B&H Photo and they said, "Its NOT recommended to add any filter over the Heliopan 82mm Center Filter." What do you folks think? Thanks in advance for your expertise.