Graduated filters, also known as neutral density graduated filters or grads, are a frequently used type of filter with digital cameras. They are used to reduce light in one section to balance the tones of an image and make it appear more natural.
About Graduated Filters
Graduated filters are similar to neutral density filters in that they reduce the amount of light that can pass through but, unlike neutral density filters which are treated all over, graduated filters are just treated at the top. They alter the tones in a scene so they can be accurately captured within the camera’s dynamic range. This means that underexposure and overexposure can be avoided. Underexposure can result in darker areas turning out almost black, while overexposure can result in lighter areas turning out almost white. Graduated filters bring out detail and present the image more faithfully to how it appears to the human eye. They are frequently employed in landscape photography and are especially useful with scenes with highly contrasting areas.
Graduated filters are available in different strengths and with hard or soft edges. These options give the photographer versatility to apply the correct filter depending on the particular shot. The treated section of a graduated filter has an opaque appearance.
While photo editing software can be used to some extent to alter digital images, the solutions offered by graduated filters are typically far more convenient and easy to apply. Exposure can be altered at a later stage on a computer, but the effect of graduated filters is usually more natural.
Choosing Graduated Filters
Graduated filters are available in different strengths, graduations, and materials and with different fittings. Choosing a filter involves considering which strength and type of graduation are most suitable for the style of photography.
Stops and Filter Strengths
Stops are terms used in photography to express a relative change in light brightness. This is linked to exposure and how much light can be captured, which in turn is dependent upon aperture, shutter speed, and ISO setting. Because aperture, shutter speed, and ISO setting are expressed in different ways, stops provide a universal way to express brightness.
One stop is either half or twice the amount of light captured. So decreasing the exposure by one stop would mean half the amount of light would be captured.
Graduated filters are available in different strengths, expressed by their number of stops. This only affects the treated, opaque section of the filter. Filters with more stops are used for images with more contrasting areas, while filters with fewer stops are used when there is not so much difference in contrast. One stop filters do not always darken areas enough to give a realistic impression of the scene, while stronger filters such as three stop filters can sometimes make some areas too dark and heavy. Experimenting with different filters will give an indication as to which is most suitable, but this will vary from scene to scene.
System Filters and Screw-in Filters
Graduated filters come in either system or screw-in models. Screw-in models are often the most popular type of filter because they can be easily attached to the lens. However, for graduated filters the system design is preferable as it allows the filter to not only be rotated, but also moved up and down. This allows the filter to be aligned correctly with the contrasting areas.
System filters, which use an adaptor ring and filter holder to attach the filter to the lens, provide this flexibility. Not only can the filter be moved as desired, but more than one filter can be placed in the holder to produce the effect created by one stronger filter. System filters vary in quality, and this needs to be balanced against available budget.
Hard and Soft Filters
Filters may either be hard or soft with regards to graduation. Hard graduation filters have a more distinct line in the centre of the filter, which separates the treated and non-treated area. They are used for scenes which have strong distinction between areas of contrast. For example, they are often used in landscapes to separate the foreground from the sky. In this case, the line on the filter would be placed against the horizon.
Soft graduation filters have a less distinct separation. They are used for scenes which do not have obvious separation in areas of contrast and where using a hard filter would result in a particular object having unrealistically separated dark and light areas. Soft graduation filters can be more difficult to place correctly.
Resin and Glass Filters
Both glass and resin filters are available, though resin filters are the more common. Resin filters have the advantages of being lightweight and more resistant to damage from dropping. However, they are also more likely to be scratched.
Using Graduated Filters
Graduated filters can be used and tested in different ways to find the most appropriate filter for the scene. Shutter speed and ISO settings can be controlled manually, and using manual settings gives the photographer the most control over exposure. Set the shutter and ISO speed according to the foreground before attaching the filter. Align the filter with the areas of contrast, which usually means placing the line across the horizon.
Alternatively, the camera’s metering system can be used to calculate light levels and adjust exposure accordingly. The histogram can be checked to make sure the right filter is being used and detail is not being lost. If the histogram has a peak in the middle and doesn’t extend to the far right, the filter might be too strong.
Graduated filters reduce the amount of light that can pass through a section of the filter, allowing tones to be captured within the camera’s dynamic range and so portraying a more realistic image without underexposed or overexposed areas. Graduated filters are often used in landscape photography, and their effects are difficult to reproduce digitally. They are available in different strengths or stops, with each stop increasing or decreasing the amount of light captured by twice as much. They come in either system or screw-in models, with system filters recommended for their flexibility which allows them to be moved up and down as well as rotated. Both hard and soft graduated filters are available. Hard graduated filters have a more distinct line between treated and untreated areas and are used for areas with strong contrast, such as foreground and sky. Soft graduated filters are used to avoid lines across objects that appear in both light and dark areas and for scenes with less sharply defined areas. There are both resin and glass filters, with resin filters more common. Buying more than one graduated filter, with a range of stops and hard or soft graduations, will give more versatility with scenes of varying composition and contrast. Research product descriptions to find the filters that are most suitable, and compare prices to find the best value filters.