The ALC-SH151 Lens Hood from Sony is specifically made for the FE 100-400mm f/4.5-5.6 GM OSS lens. The hood is made to block stray and extraneous light from entering the lens and causing lens flare. A window is located on the side of the lens hood for filter adjustment, such as a circular polarizer or an ND filter. Also, the lens hood sustains accidental or sudden impact instead of the front element of the lens, which would normally cause damage. Additionally, it can be used as a spare or as a replacement to the original lens hood.