My primary lens is a 18-70 nikkor. The filter size is 67mm. The only filters I have now are a tiffen UV and a HAMA circular polarizer. I want to get ND and IR filters. But I'm also thinking about any lense I may want to buy in the future. (If I get the nerve for it, I'l spring for the f2.8 70-200 VR). It seems that the common size is 77mm for the "pro" lenses. So... I'm thinking of buying filters in the 77mm size and a step down ring (77mm to 67mm) so I can use them on my current lens. The only drawback I could see is that I would not be able to use the lens hood with the larger filter. Should I go for it?