This filter is used to balance the brighter areas of your picture to the darker ones, e.g. lighter sky with a darker landscape. It works well with digital because although you can't place the line of density anywhere (it's fixed in the middle but can be rotated), you can later crop in you're editing to get the desired composition. Filter is glass and better than Cokin which is plastic and scratches easily. Cokin filter holder has the advantage of complete adjustability because you slide the filter in and out as well as rotate it. By the way .6 ND is equal to one stop of light, something Tiffen doesn't explain in their marketing materials. They also have half stop, two stop and three stop grad NDs. There are high quality glass filters made for the Cokin system, but they cost 2x or more than the Tiffen.