In photography, a basic distinction is made between correction and effect filters. Both reflect a small part of the incident light and thus allow less light to reach the lens. The photographer has to readjust. They do this by using the printed extension factor of the respective filter as a reference. With a factor of 2, for example, the aperture would have to be opened one step further or the exposure time doubled. The corresponding tables are provided by the respective manufacturers.
These basic settings are the same for all filters. But now we would like to introduce a few useful filters in more detail. We will show you which results can be achieved with the individual filters and for which type of motif they are particularly suitable. As mentioned before, a distinction is made between correction and effect filters:
These kinds of filters serve especially to influence the saturation, contrast, or UV exposure of the image, or to correct it.
The polarising filter is a very useful filter the effect of which cannot be imitated with Photoshop. Especially in product, architecture, and landscape photography, the polarising filter is often used to suppress reflections on non-metallic surfaces.
The filter works because it only filters out light from polarised light in a certain plane of oscillation and absorbs the other reflecting light and converts it into heat. The polarising filter is mounted in front of the lens. The effect on the light situation is adjusted by rotating the filter.
In photography, the polarising filter can be used in many ways due to its physical properties. As already mentioned, strong reflections from non-metallic surfaces can be contained. On the picture below you can see the difference. In the picture above, the water reflects very strongly and appears impermeable, in the lower picture it appears more natural. In addition, the filter produces richer green tones, as excess blue light is filtered out.
For many photographers, the polarising filter is a must-have. The small filter can be used flexibly and the user can quickly judge whether the use of the polarising filter would be worthwhile. There is no better tool against reflections.
The gray filter is also called ND filter or neutral density filter. Some also call the gray filter sunglasses for the lens. It consists of optical glass that is evenly coloured grey and reduces the incidence of light on a film or photo sensor.
Particularly with long-term shots, the dimming effect of a lens may not be sufficient to effectively reduce the amount of incident light. This results in overexposed images. Many photographers therefore resort to gray filters. The filter allows for longer exposure times or larger aperture settings without affecting the colour and contrast of a subject.
There is a table for the calculation of exposure adjustments for the use of ND filters. This is primarily based on the extension factor. A gray filter with the designation “ND 64”, for example, extends the exposure time 64 times. In other words, the photographer saves 6 f-stops.
The following image could have been taken with this filter:
In the picture the water seems to trickle from the mountains like fine sugar. This is achieved by using a very long exposure time which is made possible by the grey filter. In addition, the water surface looks very smooth. However, the gray filter does not only contribute to wiping effects on running waters, it is also used in architectural photography to make people disappear in photos. Extreme exposure times are also necessary for this, although the photos would be overexposed without an ND filter. In addition, continuous traces of light, such as those produced by moving cars at night, can be recorded.
Gray gradient filter
The human visual system can perceive differences in brightness much more accurately than modern SLR cameras. When taking pictures of landscapes, details in the sky or below the horizon may be lost even though the human eye perceives everything. This is largely due to the lack of dynamic range in digital cameras. If, for example, the sky is very bright, it can happen that there is no detail due to overexposure. In this case, even RAW images cannot be improved on the computer because the information is lost. Photographers therefore use gray gradient filters for their images.
To get a proper exposure between the lower part of the subject and the sky, use the gray gradient filter. The captured image will have a more detailed sky.
The gray gradient filter transitions can vary in strength. But they do have one thing in common – the straight, horizontal line. This is also the boundary of gray gradient filters. Objects that protrude into the motif or beyond the horizon line may also be darkened. The only remedy here is a series of exposures, which are then combined on the computer to form an overall picture.
All three filters mentioned here originate from the times of analogue photography. Their correction effects can only be recreated more or less or not at all on the computer using image processing programs. This is why many photographers swear by the use of filters.
Effect filters or creative filters are used as artistic means of design. Some filters can, however, produce very tacky motifs when used excessively. We will therefore only discuss two filters in more detail.
With this grid filter, point-shaped light sources can be transformed into quadrangular, hexagonal, octagonal, or hexagonal stars against a dark background. Spotlights are mainly spotlights. Some photographers use this effect for water reflections, for example. Others have brilliant-cut diamonds shine through a small star effect on product photos. Our picture shows that the filter can also be used at night.
These attachment filters allow either radiation of a certain wavelength to pass through or filter out certain colours. The latter, however, is rarely the case. These filters are usually made of glass, plastic, or gelatine foil. Colour filters can be used as both correction and effect filters. In this case, however, these filters are used to highlight special colours.
In the digital age, almost all effect filters can be reproduced by modern photo editing programs. With correction filters, the situation is somewhat different. In particular, polarising filters cannot be replaced by image processing programs due to physics. Ultimately, every photographer has to decide for themselves which filters to add to their photographic equipment. Here, the area of application and flexibility play a very important role.