Neutral Density Filters
(i)Neutral Density Filters - Absorptive
(ii)Neutral Density Filters - Reflective

The main purpose of using neutral density filters is to reduce the amount of light that can pass through the lens. As a result, if a shutter speed is kept the same, after adding a neutral density filter, a larger aperture must be used to obtain the same exposure. Similarly, if an aperture is kept the same, after adding a neutral density filter, a slower shutter speed must be used to obtain the same exposure.