BTR GRADUATED ND filters have variable density throughout the filter space (soft transition from light to dark followed by medium transition from dark to light). It means that the light entering the camera is reduced gradually. This is very useful in situations when some parts of the photograph are overexposed (the sky is too bright - especially at sunsets and sunrises). BTR is perfect for scenes with rugged horizon. BTR GRADUATED ND filters can be used in combination with full or graduated filters in stacking mode.