The Lee Filter System is required to use the 100mm Lee Filters and Graduated Filters.
The high quality construction of this product is well known. I love the way it works and the control it gives me when using graduated filters is awesome. I can easily adjust the gradual filter effect to get it right on the horizon of a landscape shot for example. I know you can do it in After Effects but I really like getting it as close as I can in camera.
B&H Link: http://www.bhphotovideo.com/c/product/87108-REG/LEE_Filters_FK_Foundation_Kit_Standard_4x4.html
Lee Filters: http://www.leefilters.com/index.php/camera/system#system-what
Below are two photos I took using the graduated filters.
