Gray gradient filters are a useful tool when it comes to getting the problem of dynamic range under control. It has its limits in colour fastness and odd horizon lines.
Grey gradient filters: What are they used for?
Especially if you mainly photograph landscapes, you will have noticed long ago that there is always the following problem. If the sky is correctly exposed, so that it is nicely deep blue and if necessary the clouds stand out clearly and clearly, then the landscape is massively underexposed. If the landscape is correctly exposed and all subtleties are visible, then the sky is usually only a bright surface without any structure or drawing.
This is because, unlike the human eye, the camera cannot differentiate differences in brightness so well. Both the differences in brightness (measured in f-stops) in a scene and the ability of a camera to handle them are called dynamic range. Good DSLR cameras have up to 13 f-stops dynamic range.
The problem mentioned above can be solved with gray gradient filters. The lack of dynamic range of the camera can also not be changed by subsequent image processing.
Gray gradient filter: How do they work?
A gray gradient filter now works in such a way that it is placed on the lens and thus neutrally darkens the upper part of the scene. It simply lets less light through in the upper area, ideally without influencing the colour. In the lower part it is transparent and in between there is a transition area, depending on the design, which is always a straight line.
Gray gradient filters are differentiated according to how strong the darkening is. The information is given in f-stops. It is said, for example, that the filter fades out two f-stops. While darkening by 2 to 3 f-stops is the most common, there are also filters that can darken 4 f-stops. Also the transition between the dark and the light area can be differently hard or soft depending on the filter.
Advantages and disadvantages of screw and plug-in attachments
Gray gradient filters are available as screw and plug-in versions. Screwed-on filters have the disadvantage that the transition line cannot be moved; but this is desirable because the horizon line is not always exactly where the filter wants it to be. Plug-in filters have therefore established themselves on the market; they can be moved in their slot option screwed onto the lens.
Depending on the lens and sensor size, the appropriate filter size must also be selected. All common sizes are available on the market.
Gray gradient filters are useful tools to get the dynamic range of a scene under control. But of course they also have their limits. For example, the horizon line is not always a straight line (for example in the mountains).
In addition, even high-priced specimens are rarely to never colourfast. An alternative to the gray gradient filter is, of course, to make several exposures of the scene (bracketing) and then to superimpose the individual shots digitally later. This assumes, however, that there are no moving objects in the scene, as otherwise the images cannot be superimposed on each other.
Working with the gray gradient filter needs some practice. There are two points you need to consider. One is the strength of the filter. You must be able to estimate the dynamic range of the scene well and reliably so that you can choose the right strength to achieve optimal contrast. On the other hand, you must place the transition correctly so that the image does not appear unnatural. As always, the magic word is: practice!
Result: Gray gradient filter darkens the image slightly, but requires some practice
Gray gradient filters help with the problem of dynamic range. They have their limits with the color fastness and with odd horizon line (for example in the mountains). An alternative is the digital superimposition of different exposures of the same scene. However, this assumes that there are no moving objects in the scene and that the camera does not change its position (tripod).