If you love to shoot outdoors on bright sunny days with a shallow DOF, you'll need to get yourself an ND (neutral density) Filter. The ND filter will cut down the amount of light that comes in through the lens so that you can tame that shutter speed, and use a wide aperture without blowing out the image. Still confused? Olivia has a short video that explains how shutter can change the look of your video here: http://vimeo.com/25851113.
There are static ND filters in various sizes and densities, and then there are Variable ND filters. The convenience of a Variable type ND filter is you can simply dial in how much light you need to block out. Variable ND filters are a two piece glass filter design. Rotate the outer glass, and it will increase/decrease the amount of light passing through.
One important thing to know is that you will get different results from different Variable ND filters on the market. Because the filters are using two pieces of polarizing glass, you could suffer from color cast (reddish/purplish), also color shifting (color temp changes as you rotate the filter), and more importantly Softness of image. The more expensive ones don't suffer as much with these problems, but they can be out of reach for most hobbyist. Of course, I use what I can afford, because in some situations I feel anything is better than nothing. If you're a stickler on quality, or invested thousands of dollars on that Zeiss and Canon 'L series' glass, I think you'll want to try to maintain the best image possible by using something of higher caliber.
Shown throughout this article is the latest 77mm LCW Digi Pro HD, which on the outer end terminates to a larger 82mm. This step up from 77mm-82mm design prevents obstruction when used on wider lenses. Packaged well, the LCW Digi Pro HD comes with it's own padded case and an 82mm Lens cap if you choose to leave the filter on during storage. To ensure the filter does not accidentally rotate during use and changing exposure, there's a locking pin to hold position.
Light Craft Workshop was one of the first companies to really hit the DSLR Video market with a quality Variable ND filter about 3 years ago. Since then, they've improved with an Ultra Mark II version, and now has released a much more improved Fader ND Digi Pro HD. The Digi Pro HD filter was first released in a 4x4 filter used in Matte Boxes, and has now been adapted to this variable threaded filter.
I was lucky enough to have this sent over from LCW [Thanks Guys], and will be taking it out for some use. There's no question in my mind that it will provide top quality results, and i'll try to provide some still images at different focal lengths for you all. The new Digi Pro HD filter was just announced a few days ago, and may not yet be available, but you can see all their announcements at their website here: http://LightCraftWorkshop.com. As this Digi Pro HD is not a replacement for some of their other Variable ND products, you can find those products and prices already available at their official store via eBay (click here).
Light Craft Workshop Variable ND & CPL Filters