The Sigma A00090 Rear Filter Holder is designed to enable the use of either a Sigma 46mm Normal Rear UV Filter or a Sigma 46mm Rear Circular Polarizing Filter with select Sigma lenses. After either of those filters are screwed onto this filter holder, it can then be placed into a Sigma 300mm f/2.8 EX, 300mm f/2.8 EX DG, 500mm f/4.5 EX DG, 800mm f/5.6 EX DG or a 300-800mm f/5.6 EX DG lens.
When placed within a compatible lens, this Sigma rear filter holder, which features a cast-aluminum construction, is secured or released through the use of its squeeze-lock mechanism.