Suitable filters for weather photography

Landscape photographers use many types of filters, some being very expensive. Luckily, with weather photography you don't need many kinds of filters. Often, only a polarizing filter is sufficient. In fact, a polarizing filter is all I use for my photography, except for photographing the sun, with which I use a neutral density filter.

Filters such as warming filters or gradient filters are little useful for weather photography. Since you don't need to see detail in the foreground at all in weather photos, gradient filters are not required.

One other type of filter that may be useful is a UV filter, simply because it will protect the lens surface from being damaged. But keep in mind that any filter will add extra reflecting surfaces to the optical path through the lens and camera.

Polarizing filters

There are two types of polarizing filter: linear and circular. These filters work the same way in that they filter out light of a certain polarization. A circular polarizing filter is useful for SLR cameras that use a mirror when light metering. A circular polarizing filter consists of a linear filter and a circular polarizer after that, to make the light circularly polarized and therefore its intensity won't change after subsequent reflections. If in doubt which one to use, use a circular polarizing filter.

The filter is rotatable, and it has a mark that indicates the axis of polarization.

Polarizing filters are extremely useful if you want to photograph the weather, since they will often add contrast to the sky and clouds, the rainbow, and many halo phenomena. Usually you use the filter for the blue sky, since the blue sky is polarized. By blocking some of its polarized light out, the sky is darkened, and the contrast between the sky and an unpolarized cloud is enhanced.

The sky is maximally polarized 90o away from the sun. If you use a polarizing filter in combination with a wide-angle lens, you will notice the brightness changes across the frame.

Some remarks about polarizing filters:

• Since the polarization directions differ under all circumstances, you will have to see every time how much to rotate the filter on the lens to obtain optimal contrast.

• Care must be taken if you photograph with blue sky overhead at high altitudes, because the sky can be almost 100% polarized and can be made to look black on photos.

• If in an airplane, you cannot use a polarizing filter to photograph the clouds and such, because the airplane windows are birefringent (the amount of polarization depends on the wavelength), and you will see many colors.

• Some types of glass also cause polarization due to stresses in the glass. A typical example is the patchy structure you sometimes see on car rear windshields if you look at an angle. Such glass in combination with a polarizing filter also causes undesirable results.

The birefringence of airplane windows renders any kind of polarizing filter useless.

Neutral density filters

These are only useful if you need to photograph something in the sky very close to the sun, like a corona or iridescence. But most modern cameras have fast shutter speeds such as 1/4000 second, and then these filters are not required.

The only neutral density filter that is useful to have is an ND5 filter that transmits 0.001% of the incoming light (a fraction of 10^-5). These filters are useful if you want to photograph or observe the sun during the daytime, like a partial solar eclipse, multi-sun exposure, or when photographing sunspots with a telescope.