This specifically design Filter Holder that is fitted with WR Circular Polarizer Drop-in filter is only compatible with Sigma 500mm f/4 DG OS HSM Sports Lens, where the filter holder will fits into the rear slot of the telephoto lens and locks into place, it also features a small wheel that can be adjusted so you could get your desired effect from the circular polarizer. It is also has a filter factor of 2 to 4x meaning you can increase your exposure by 1 or 2 stops.