Full Mediterranean colors large viewThe Hoya ND 400 filter is a ND (neutral density) filter which reduces the light entering the lens by 9 f stops. That means that exposure time is multiplied by 512. In other words if your shutter speed without any filter was 1/30s, with the filter the shutter speed will be around 17s.
As you could notice, for this springtime i do many seascapes, mostly with long exposures. Without any filters, such exposure times are only possible some few moments at dawn and dusk time. The ND 400 is a good tool to increase the time available for long exposures and such shots with scenes a little more lightned can be beautiful and unusual.
Of course, with or without filter, shooting scapes at noon won't give stunning images but a strong ND filter can open some creative doors to capture beautiful lights with an unusual style.
Last point : The ND 400 is a very dark piece of glass (i could say black) and when it's on the lens you don't see anything in the viewfinder. So it's not for point and shot photography. You have to set up the tripod and the camera, frame without filter, lock everything on the tripod, install the filter, shoot, remove the filter and so on.