Cokin P Series Hard and Soft-Edge Graduated Neutral Density Filter Kit with P Series Filter Holder
Gradual neutral density filters reduce the amount of light reaching the sensor. They allow you to decrease the shutter speed in order to achieve motion blur, and/or to reduce depth of field in very bright conditions, also in video mode. Simply by rotating the filter holder you can adjust the position while framing. As they are neutral they don't affect color rendition; their effect can be cumulative.