One of the unique things you can do with the Sigma Sd14 is capture infrared photos. This is new to me and over the holidays I had some time to play. I used a R72 visible light filter and also two linear polarize filters stacked together. It was cold out, about minus 10 so I didn't spent too much time or thought. I need to find out more about where to focus. There is info on the Sigma SLR forum found at dpreivew.