I found a cool tutorial on JoÃ£o P. Ribeiro’s site. In his shots he is using a Hoya R72 filter. I’ve purchased one for myself off ebay and will have some samples of my own in the coming month or so.
His tutorial is very well done and is in-depth. I look forward to going through it a couple more times before I get my filter and see what sort of interesting shots I can come up with.