How does a polarizing filter work?
The light naturally oscillates in three dimensions. Light rays are emitted by a light source, reflected by other objects and absorbed by some surfaces. As the light rays move through the room, they therefore oscillate in three dimensions. A polarizing filter ensures that light no longer oscillates in several planes. It converts the light so that it only oscillates on one plane. In addition, each polarizing filter can be rotated so that the direction and degree of polarization can be adjusted by turning it.
Why do you need a polarizing filter?
A polarizing filter is always used by photographers when one wants to avoid reflections.
Photographing through the water surface with a polarizing filter
For example, if you want to photograph the fish in a body of water, there are often reflections of the sky or trees on the water surface. Therefore the fish are not or hardly to be recognized on the photo at all. With a polarizing filter on the camera these reflections of the sky on the water surface are almost completely eliminated, so that the fish are clearly visible in the picture.
Improve colours in landscape photography with a polarizing filter
Another common problem is that especially on cloudy days the different shades of green often look very similar in nature. With a polarizing filter you can create bright colors here. The reason for this is that the sky is also reflected on the leaves. The surface does not reflect as much as for example water, but the white of the sky is reflected here as well. This means that the green tones are not as strong as on a sunny day. So by using a polarizing filter on the camera, you can avoid the reflections and create more colorful images. This effect of the polarizing filter can be used in almost all areas of nature photography.
Using a polarizing filter to enhance the contrast and the blue of the sky
If a subject is at a 90° angle to the sun, a polarizing filter can be used to enhance the blue of the sky. Together with the previously mentioned point, excellent colours and contrasts can only be achieved with the help of this filter.
What distinguishes circular polarizing filters (CPL filters) from linear polarizing filters?
A "normal" or linear polarizing filter, which behaves according to the theory described above, only allows light of a certain polarization direction to pass, whereby the direction of the light is irrelevant. Unfortunately, however, light metering systems of SLR cameras have difficulties with linearly polarized light and can therefore give wrong results. To avoid this problem, circular polarizing filters are used. These also filter out light of one polarization direction, but "circulate" the polarization in the direction of the camera. For the measuring systems of the cameras, this is almost as good as if the light were to enter unpolarized. A circular polarization filter in front of the lens therefore serves the same purpose as a linear one, but avoids possible problems. Consequently, both variants can be used for analog photography, whereas a circular polarizing filter must be used for digital photography.
What do you have to consider when buying a polarizing filter for photography?
First of all, you have to be sure with which lens the polarizing filter should be used. Often, the standard zoom, for example the 18-55mm, comes into question. In this case, you can read on the lens or in the lens description which filter diameter the lens has. Common sizes are 49mm, 52mm, 58mm, 62mm, 67mm, 72mm, 77mm and 82mm. The polarizing filter is then needed to match this size.
Is it possible to use one polarizing filter with different lenses?
Yes, of course it is possible to use one polarizing filter for several lenses. It is necessary to work with a step-up ring . You should buy the polarizing filter for the lens with the largest filter diameter. With the Step-Up-Ring you have an adapter between the different filter thread diameters.
How much light does this filter absorb?
A polarizing filter allows less light to pass to the camera sensor due to the way it works. A rule of thumb is that the polarizing filter absorbs about two apertures of light. This can be a disadvantage, because depending on the light situation, you may have to use a tripod or increase the ISO. On the other hand, it can also be an advantage if the motif is perhaps shown to its best advantage with a somewhat longer exposure.
Can I always leave a polarizing filter on the lens?
Yes you can, but it is not recommended. As described above, the polarizing filter absorbs light. So the captured image is darkened, which leads to longer exposure times. The effect of this filter is also not desired in all situations. Therefore it is recommended to use the filter only if the effect is really desired.