The CPL filter, also known as the circular polarizing filter, is mainly used to eliminate harmful non-metallic reflected light, increase color density, deepen the blue sky, highlight white clouds, make the image more transparent, improve the clarity and expressiveness of shooting. It is also often used to film behind glass, transparent water and underwater creatures.
The ND filter is a neutral density filter to reduce the amount of light that reaches the camera sensor, so that the correct exposure value can be selected and overexposure avoided. It can also “resist” a large amount of diffused light, which can improve the saturation of the image color and make the image more transparent. The use of an ND filter can also allow you to use longer shutter speeds to capture special effects such as foggy water, night-time light traces and more.