For very bright motifs in the snow or on the beach the aperture would also have to be closed, despite minimum exposure time. This would mean losing the option of short depth of field, e. g. for portraits. ND filters can produce wipe effects in movements if the exposure time can be extended with the required aperture. A waterfall then no longer appears to be frozen, but as a flowing motion. ND filters create ingenious effects in architecture or urban photography. With long exposure times of several hours, people walking through the shot are blurred or not reproduced at all.