Cokin Neutral Density Filters will allow you to gain the 1, 2 or 3 apertures you need to allow you to play with backgrounds, distance and depth of field. This Cokin P153 Neutral Density P-Series ND4x filter will reduce the amount of light reaching the film but without affecting the colour balance. An ND4x Neutral Density P-Series filter has a progressive graduation from the middle to the top of the filter. It is the same colour as the ND2x filter but with a lower tone and will allow a 2 stop shutter speed / aperture decrease. Neutral Density Filters allow you to use the low speeds you need to give an impression of motion.