The HOYA Variable Density filter provides a convenient way to maintain exposure control by being able to vary the amount of light entering the camera by 1.5 to 9 stops (0.45 to 2.7 density for Cine use). The precision built-in double ring design allows the outer ring rotates to control amount of neutral density effect anywhere within the 1.5-9 stop range. This double-ring design is also thin to reduce the likelihood of vignetting with wide-angle lenses. This control allows for many special effects such as being able to control depth of field by using a wider aperture or create or control motion blur by being able to choose just the right slower shutter speeds for perfect blurring.
The HOYA Variable Density filter can take the place of a range of graded ND filters which saves money by only needing to buy one filter and saves time on location or on set by not needing to change filters constantly to change the effect, just turn the right to get the effect you want. The HOYA Variable Density filter puts you in control.
An example: The if your normal exposure without the filter is 1/250 of a second at f/11 the and you mount the filter and set it to the "Min" setting, then your exposure will be 1/90 of a second at the same f/11 or it could be 1/250 of a second a f/6.5 depending on which setting you want to control. If your desired effect is motion blur in the picture then turn the filter ring and watch your shutter speed drop in camera. At Max setting a shutter speed of 2 full seconds (9 stops) is possible at the same f/11 aperture.
This is an especially useful tool when creating motion blur in moving water such as waterfalls, rivers and crashing waves. Other examples of good times to use very slow shutter speeds to create blur are; moving vehicles, trains, cars and congested city traffic; blurred panning effects where the subject, a runner, bicyclist or car is clear but the background around it is blurred from the camera following it's movement.
Variable Density filters, and ND filters in general have these main uses:
Slow down shutter speed for motion blurring effects like waterfalls, cars or blurred panning movement to make the subject stand out from the background.
Allow wider apertures to be used to decrease depth-of-field, literally focusing more attention on the subject.
Allow higher ISO films to be used in brighter lighting conditions.
Allow cine/video cameras, which have a fixed shutter-speed range, to film on brighter lighting conditions such as the beach or in snow on a sunny day.
The HOYA Variable Density filter uses high-quality optical glass from Hoya Corporation, the worlds largest optical glass manufacturer and is available in sizes 52mm to 82mm.
For best results HOYA recommends using a tripod when photographing with slow shutter speeds.