Photographing solar eclipses and ultra-bright light sources can be extremely dangerous. This filter reduces light values by 9 stops to less than 1/500th of its original intensity and allows safe photography. It can also be used to achieve super slow shutter speeds in daylight to render moving subjects invisible.

With Tokina AT-X 116 PRO DX-C, HOYA ND400  F/16 at 30 seconds