ND Filter Factors, Densities and F-Stops compared

Numerous manufacturers use different terminology for their Neutral Density filters, which can sometimes make direct comparisons difficult. I’ve produced this chart showing the various designations in use against the number of stops reduced. Some manufacturers produce filters that fall in between stops, making comparisons even harder. For example, an ND400 filter would be just below 9 stops, but probably within tolerance to be marketed as a 9-stop filter.

Those highlighted are the three most versatile filters overall, though it depends on your intended use. A 15-stop filter for long exposures in bright conditions, fully blurring clouds and smoothing seas, might be more useful than a 10-stop, which may only partially blur in the same light. Bear in mind that light levels and chosen ISO and aperture settings affect the outcome.