What is a gray graduated filter (Graduated Neutral Density / GND filter)?
Graduated gray filters are glass filters that are clear on one half and darkened on the other half. These two areas converge in the center of the filter, going from dark to clear. This transition varies depending on the type of filter. GND filters are used to balance the exposure of a scene that, especially in landscape photography, consists of a lighter section (the sky) and a darker section (the foreground). The human eye makes it possible to visualize a wide range of light and shadow. This is also known as the dynamic range of a scene. Unfortunately, today's camera sensors are not able to reproduce the dynamic range as the human eye is able to. The use of GND filters helps to give the sensor a helping hand. This makes it possible to capture the dynamic range of a shot with a single exposure.
What Are the Different Types of GND Filters and When Should You Use Them?
Soft GND filter
These filters have a very smooth transition from transparent to dark. They are suitable for scenes that have a broad or broken transition from the sky to the actual foreground. An example of a scene that should be shot with a soft GND filter is a mountain landscape crossing the horizon line. A rock formation in the sea is also predestined for photography with the help of a soft GND filter.
Hard GND filter
These types of GND filters have a hard transition from clear to dark. They are suitable for scenes that have a strongly visible transition from the sky to the actual foreground. This filter is most useful for landscape shots in which no elements extend beyond the horizon, such as sea shots with a wide view of the ocean. Also, these filters can be used when a hard transition against the sun is beneficial.
Reverse GND filter
Reverse GND filters with a "reversed transition" are similar to the hard GND filter except that the darkest part of the filter is in the middle. These filters are for shots that are taken against a light source and where the light is most intense on the horizon.
Medium GND filter
Medium GND filters are similar to the filters with a smooth transition, but the gradient is not quite as smooth. These filters are the most versatile and can be used in most situations to shoot away from or against the sun.
In which situation are gray gradient filters useful?
What appears differentiated and high-contrast to the human eye, such as the sky, can still look like a gray mass in the picture. Because if a subject has a high dynamic range, i.e. very bright and dark areas at the same time, a gray gradient filter is able to compensate for this high dynamic range directly during the recording. An alternative to this would be digital post-processing on the computer. Two images are merged into one image. However, the result is usually not nearly as good as when recording with the help of a gray gradient filter. In addition, the appeal for most photographers lies in capturing an almost perfect image in just one shot. It's not half as fascinating to achieve the result by piecing together different images. Because the attraction of photography lies and has always lay in the best possible and most creative compromise.
Is there a difference between gray graduated filters and graduated filters?
As the name suggests, both types are gradient filters. Graduated gray filters have a gradient from gray to transparent. However, there are also filters that go from one color to transparent. In the 1980s, for example, tobacco graduated filters were very popular. Nowadays, however, colored gradient filters are hardly ever used because this effect can be created on the computer with little effort.
Why do you need a gray gradient filter?
A gradient filter is used to neutrally darken the light part of a photo, usually the sky. This enables the camera to capture almost the entire dynamic range of a landscape. A camera gets, so to speak, an extension of its capabilities through the gradient filter. As mentioned above, there are other tools, mostly in post-processing, to recreate the differences between lighter and darker areas in a photo. Nevertheless, gradient filters in landscape photography cannot be completely replaced by image processing. One could even say that the use of graduated filters is essential for landscapes. When major post-processing is to be avoided.