Hi, I'm new to digital photography and recently (~2 months ago) bought a 450d and have picked up a few lenses (kit, 50 1.8, 55-250 IS). I've just been reading about filters, specifically polarizing, and discovering the effects they can have to your shots. Is there any restrictions on what filters will fit on canon lenses. I can see that the diameter of the lens is important - so for me I would need either 52mm or 58mm depending on which lens(es) I want to use the filter on, but other than that can I just buy any filter? Specifically I'm looking on the Hoya PRO1 Digital Circular PL Filter, although I've been googling this and have just come across a thread on another forum where someone is talking about the lens cap not fitting over a hoya filter? Would I be better going for canon branded filters? Will the lens cap fit over these?