Nd Filter
A neutral-density (ND) filter reduces the light entering the lens by a stated amount, without changing color, letting a photographer use a longer shutter speed or wider aperture than the ambient light would otherwise allow. Filters are typically labeled by stops (a 6-stop ND), by density factor (ND64, which is also 6 stops), or both, since the two labeling conventions coexist across different manufacturers.
Each additional stop of ND density doubles the shutter speed needed to hold the same total exposure — a 10-stop ND (commonly labeled ND1000) turns a fast daylight shutter speed into several seconds, the standard tool for smoothing water or clouds in bright conditions where narrowing the aperture alone can't reach a slow enough shutter speed without diffraction softness.
Frequently Asked Questions
Can my camera meter accurately through a dense ND filter?
Usually not reliably past roughly 6 stops of density — most photographers meter the scene without the filter attached, then apply the stop-based correction manually before attaching the filter and shooting.
Does an ND filter affect depth of field or only exposure?
Only exposure — it reduces light without changing your chosen aperture, so depth of field stays exactly what your real f-number would produce with or without the filter attached.