A Neutral Density filter, commonly called an ND for short, acts a bit like sunglasses for your lens to block out light and extend your shutter speed, or to control lightflow when shooting video. A Variable Neutral Density (VND) consists of two polarising filters which when turned against each other reduce the light flowing in through the lens and hitting the camera sensor.
Doing so has many useful applications for both photography and videography, including achieving slower exposure times in still images to create movement. They're also handy for controlling the light when you’re shooting video as the shutter speed will be fixed, where changing the ISO or aperture would have an adverse effect on image quality and depth of field. I got hold of Tiffen’s Variable ND filter, first launched back in 2011, and put it to the test to see if you should add one to your kit bag.
