Silky water effects, streaked clouds, motion-smoothed with an ethereal look; long exposure photography seems to be in vogue as photographers discover the looks that can be created. There are multiple ways to achieve this. The most basic is to buy a standard neutral-density photography filter which cuts the light, allowing you to use long shutter speeds without overexposing your shot. You can achieve exposures minutes long, especially when using 10-stop ND filters like the Lee Big Stopper or even the 15-stop Super Stopper. I…