Graduated Neutral Density filters are rectangular in shape, and clear in the bottom portion of the filter before transitioning into the neutral density portion near the center of the filter. The purpose of a graduated ND filter is to reduce the brightness of selected areas of the frame, balancing out the exposure throughout the image. The rectangular shape of the filter allows you to adjust the positioning of the graduation in your image to achieve your desired results.
How sharp the transition between the clear and neutral density portions of the filter determines the type of graduated filter.
Graduated filters are available in the following filter types:
- Soft Edge Graduated Filter: Soft Edge Grads have a tapered transition from the clear to neutral density portions of the filter, resulting in a filter that can be used in any landscape setting, but is particularly useful when the landscape has various elevations such as hills or mountains.
- Hard Edge Graduated Filter: Hard Edge Grads have a fixed transition line, resulting in an abrupt transition from the clear to neutral density portions of the filter. Hard grads are ideal when the horizon line is flat, such as the ocean.
- Medium Edge Graduated Filter: Medium Grads fall right between the soft and hard edge filters. The transition between the clear and neutral density portion of the filter is less tapered than the soft grads, and not as abrupt as the hard grads. Medium grads are an excellent choice for both settings where a soft or hard grad would be used.
- Reverse Graduated Filter: Reverse graduated filters have the same fixed transition line as a hard edge filter, but are strongest at the center of the filter before tapering off towards the end of the filter. Reverse graduated filters are ideal for sunrises and sunsets, where the brightest light is concentrated near the horizon line.