Hi Paul, unlike Clive I have protection filters on all my lenses, and yes, I also have insurance as well. Over the years it has saved my lenses on several occasions - a bust lens in the middle of a shoot upsets you and more importantly - the client. For a 10-20 you will need the "P" series Cokin holder and filters and you will still get marked vignetting at the wider end. I used a 10-20 Sigma for DX cameras and still use a 12-24 Nikkor on FX. The Nikkor cannot take filters unless you use a "Lee" holder - although Cokin have promised one, I've not seen it. The Lee holder costs almost as much as the lens. For landscape however, use a tripod and hold the filter in front - it does work.