More Info on ND Filters For The Fuji X-Pro1 | Patrick Leong
Generally, the wider the aperture, the more light that you let into the lens. The problem with this is, in broad daylight, there is too much light resulting in overexposure if I choose to shoot at a wide aperture. I could adjust the shutter speed to compensate but there are many situations where the shutter speed on my X-Pro1 just isn’t fast enough (max speed is 1/4000 of a second on the X-Pro1). This is where my ND filter comes into play.
See on findingrange.com