Whereas the neutral density grad features an area of transition where the dye fades to clear, a standard neutral density filter is coated evenly all over. Standard neutral density filters for the SW150 Mark II system come in the following strengths: 0.3 (1 stop), 0.45 (1½ stops), 0.6 (2 stops), 0.75 (2½ stops), 0.9 (3 stops)
These filters are extremely useful for bringing shutter speeds down to a useable length – for example, when shooting into the sun. They are also versatile, in that they can be stacked one on top of the other, to lengthen the exposure even further. As with neutral density graduated filters, they can be used in conjunction with other types of filter (a polariser or a warm-up, for example), for increased versatility.
However, they aren’t useful only for extending shutter speeds. They can also be used to bring down ISO ratings and to allow the photographer to use a wider aperture. For example, if your meter reading suggests an aperture of f/8, fitting a 0.9 ND standard filter would allow you to open up the aperture by three stops to f/2.8, allowing you to selectively focus and draw attention to the most important element of your composition.