The Hoya Variable Density II is an adjustable density filter with an ND range of 1.5 to 9 stops (ND3-400). The filter features a rotating frame with a convenient knob for better operation. Variable density filters are widely used because they can replace a set of fixed ND filters by providing a density range that can be adjusted depending on the desired exposure settings. For still images, variable density filters shorten the shutter speed according to the photographer's intentions when the shutter speed cannot be shortened due to camera limitations. Variable density filters can also enhance the boke effect when shooting in overexposed environments, preventing overexposure of the image. When shooting video, it is important that the shutter speed matches the frame rate set. That is, it should be equal to twice the frame rate for optimal results. This is because, unlike still photography, too fast a shutter speed can create a distracting effect and produce afterimages that don't look good in the finished video. As you can see in the image below, unlike a still image, a video clip consists of a sequence of still images. With a fast shutter speed, the individual still images blur but look consistent in the video sequence. In contrast, a slower shutter speed captures objects solidly and sharply, but in a video sequence, all objects appear separate, resulting in distracting and unnatural-looking motion. By using variable density filters, the shutter speed can be set to the right value to get the natural and smooth motion desired in video footage, as shown in the following image.