I love long exposure photography- it makes the water flowing around shores, waterfalls and rocks look smooth and silky. It also makes the clouds look streaked. For a year I've been trying to get good long exposure photos. At first I used a 10 stop variable density Hoya filter. This didn't work well during the day- there was too much vignetting. Next, I tried a 15 stop Lee filter. This was better, but there was still vignetting. I recently bought a Formatt Hi-tech 16 stop Infrared filter and I love it. It filters infrared light and this makes the colors look so nice. It comes with a light sealing case which prevents light leaks and color shifts during long exposure times.
Now I have many ideas of how to use this filter and hopefully many fantastic photos!