This 77mm Variable ND Filter from Tiffen offers a unique way of maintaining control over your depth of field and presents an efficient way to create special effects. Designed with a built-in rotating ring that controls neutral density ranging from 2 to 8 stops (0.6-2.4), it allows heavier density for a slower shutter speed. The longer exposure allows the shutter to remain open long enough to record the same amount of light, but will also create movement within the shot. It eliminates having to buy and carry around individual neutral density filters. With this one filter, you can rotate to the degree of ND you want, saving money and time.