Neutral Density filters
If you are shooting in bright sunlight you may find that you are unable to set a shutter speed slow enough to introduce some motion blur. In such cases you will have to use a neutral density (ND) filter. This absorbs light, reducing the amount of light that reaches the camera’s sensor, thereby allowing you to set a slower shutter speed.
Filters absorb different amounts of light depending on their density. For motion blur images, the most commonly used filters range from the ND8 (which reduces the light by 3 stops) to the ND64 (which reduces the light by 6 stops).
Bear in mind though that, when you start to lose light, some focusing systems perform better than others. If you use a filter that blocks out too much light, your camera may struggle to achieve focus on your subject, especially with the older Live View systems of DSLRs pre-2012.
No filter?
If you don’t have an ND filter, you can obtain a longer shutter speed by setting a low ISO, such as ISO 100, and a small aperture, such as f16 or f22. Apertures smaller than this are not usually recommended as there is a fall-off in image quality caused by diffraction.
If shooting on an overcast day, or in the shade, you can achieve the relatively slower shutter speeds required without needing an ND filter.
