The ND8 filter helps you to reduce the amount of light coming into the sensor.
It gives you the freedom to create your own work by allowing you to have more control of the camera's aperture, exposure time and sensor sensitivity settings.
Effectively, the ND4 filter helps to avoid overexposed photos.
The ND8 filter passes through 1/8 of the incoming light. This is equal to 3-stop filter strength.