10-Stop Neutral Density (ND) Filter Comparison: B+W vs NiSi
Mention B+W and if the person listening didn't hear properly he may mistake you for talking about cars. In the context of photography though, everyone knows this brand is synonymous for their quality glass filters. What kind of filters you ask - UV (Ultra-Violet), Circular Polariser and Neutral Density filters.
Most are familiar with UV filters as these are purchased not so much to reduce UV, more to protect the lens investment. The others are used as light modifiers to control or change the way and amount of light captured by the camera sensor. The favourite filter amongst landscape photographers is the Neutral Density (ND) filter. It is actually necessity for modifying the light especially in situation where the composition has a wide degree of brightness between areas of the scene. The standard ND filter has a constant darkness across the filter. A related filter is the GND (Graduated Neutral Density) and it is available in a 'Soft' or 'Hard' edge. The GND has a decreasing darkness across the filter. This makes the GND good for photographing scenes different brightness like that of the sun rising against the horizon and the dark foreground. In instances of irregular foreground objects most users like to use the 'Soft' graduated ND filter. That's a whole other debate so let's move on.
By decreasing the amount of light entering the lens, the length of time that the shutter has to be open is increased (longer time in tenths or even whole seconds). A side effect of longer exposure times leads to special effects. The effect creates a motion like blur for the scene on objects that are in motion. A good example of this is the movement of water like that of a waterfall or even that of the sea. When captured in a long exposure the water looks creamy white or whatever the base primary colour of the water is unless there's a lot of white foam/bubbles.