I want to step up the quality of my photographs of sunsets and sunrises. Of the landscape images that grab my attention on sites like Flickr, the ones I mark as "favorites" often are made with said filters. Things I want to know: hand held in front of lens vs mounted on frames? screw on filters such as a Vari ND $ingh Ray...worth it and easier to use? Any input is appreciated. thanks, erno.