I was doing some reading a few days ago about the Canon macro flashes, and I noticed there were quite a few complaints about how the flashes will not attach to the lens if there is a filter on it. Is this true? My 100 mm macro lens is brand new, so I'm very protective of it and I don't want to take the filter off to use a flash with it. Someone was telling me yesterday that I can use a Nikon macro flash (specifically, the twin light kind) with a Canon camera, which I what I think I will have to do if the only other option is taking the filter off. How would I go about doing this? I don't know much about camera flashes, so any info anyone has will be of great help. If I did use Nikon slave flashes, how would I get them to go off? This is just for future reference since I'm still saving up to buy a flash, but I want to know what all my options are. Thanks in advance!