What is a gray scale filter (Graduated Neutral Density / GND filter)?
Gray graduated filters are glass filters that are clear on one half and darkened on the other half. These two areas converge in the middle of the filter, from dark to clear. This transition varies depending on the type of filter. GND filters are used to adjust the exposure of a scene which, 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 called the dynamic range of a scene. Unfortunately, today's camera sensors are not capable of reproducing the dynamic range in the way the human eye can. In order to help the sensor, the use of GND filters helps here. This makes it possible to capture the dynamic range of an image 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 wide or interrupted transition from the sky to the actual foreground. An example of a scene that should be captured 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 a soft GND filters.
Hard GND filter
These types of GND filters have a hard transition from clear to dark. They are suitable for scenes that have a highly visible transition from the sky to the actual foreground. This filter is most useful for landscape shots in which no elements project beyond the horizon, for example, shots of the sea with a wide view of the ocean. These filters can also be used when a hard transition against the sun is advantageous.
Reverse GND filter
Reverse GND filters with an "inverted 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 taken against a light source and where the light is most intense at the horizon.
Medium GND Filter
Medium GND filters are similar to the filters with a smooth transition, but the transition is not quite as smooth. These filters are the most versatile and can be used in most situations to take pictures away from or against the sun.
In which situation are gray graduated filters useful?
What appears to the human eye to be differentiated and rich in contrast, such as the sky, can still look like a grey mass in the image. This is because if a motif has a high dynamic range, i.e. has very bright and dark areas at the same time, a gray graduated filter is capable of compensating for this high dynamic range directly during shooting. An alternative to this would be digital post-processing on the computer. Here two images are merged to one image. However, the result is usually not as good as when using a gray gradient filter. In addition, the attraction for most photographers lies in capturing an almost perfect image with just one shot. It is not half as fascinating to achieve the result by tinkering together different images. Because the attraction of photography is and has always been the best possible and most creative compromise.
Is there a difference between gray gradient filters and gradient filters?
As the name suggests, both types are gradient filters. Gray graduated filters have a gradient from gray to transparent. However, there are also filters that gradient from one color to transparent. In the 80s, for example, graduated filters for tobacco were very popular. Nowadays, however, colored gradient filters are hardly used anymore, because this effect can be created with little effort on the computer.
Why do you need a gray gradient filter?
A gradient filter is used to darken the bright part of a photo, usually the sky, in a neutral way. This allows the camera to capture the dynamic range of a landscape almost completely. The gradient filter gives a camera an extension of its capabilities, so to speak. As already mentioned above, there are also other tools, mostly in the post-processing, to reproduce the differences of brighter and darker areas in a photo. Nevertheless, gradient filters cannot be completely replaced by image processing in landscape photography. One could even argue that for landscapes the use of gradient filters is indispensable. If you want to do without extensive post-processing.