content: I think every lens which takes front-mounted filters should have a UV filter like this permanently fitted. It doesn't make a difference to the light, but it's excellent protection - if something hits (or even just scratches) the end of my lens, I'd much rather replace a $10-$20 filter than a $360 lens (which is what I've got this one attached to). Even getting a lens repaired (if you're lucky and that's even possible) is more expensive than just replacing a filter.The only exception to this general rule is for really cheap lenses - it's hardly worth buying a $20 filter to protect a $100 lens like the (excellent and highly recommended) 50mm f/1.8, for instance.