About the Polarizing Filter

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About the Polarizing Filter

Is it worth having a polarizing filter?

Of all the filters available, a polarizing filter is the first one you should buy to improve your landscape photography.

Well, the second one actually. You should start off with a basic UV filter on every lens. This will filter out unwanted ultra-violet light which can give an unpleasant blue and cold cast to images.

A UV filter will also penetrate a certain amount of distant haze.
Thirdly, a UV filter will protect the front lens element from dirt and scratches.

Apart from that, the polarizing filter is the most important filter to have.
A polarizer will darken blue skies giving them a richness they might lack otherwise.

best polarizing filters

Its other main function is to reduce reflections. This is particularly useful when photographing rivers and lakes. Reduce the reflections and flare off the surface of water and suddenly you can see to the bottom of a river.

Reflections off road surfaces can also be cut down a great deal. The same applies to foliage; leaves are less shiny and have a richer green.

Finally, in many situations colour saturation is increased a little by the use of a polarizing filter.

How to use a polarizing filter

Most polarizers screw on to the front of the lens. The filter itself is rotated in its mount. It needs to be rotated manually until the strongest effect is found. The front element of most lenses does not move during focusing, so this is no problem. With some cheaper lenses, however, the front element will rotate while the lens is focusing. With such lenses, focusing should be done first, perhaps manually, then the filter should be rotated.

When using a polarizer on the sky, the filter is rotated until the blue sky goes to its darkest. The filter will not be effective in all parts of the sky. It works best in that portion of the sky which is at an angle of 90 degrees to the sun; that is, when the sun is at right-angles to your viewing position.

Turn the filter slowly in order to find the optimum position more accurately. The same applies when using the filter against reflections. Rotate the filter gradually to find where the reflections and flare are the least. Reflections might disappear altogether but this is not always the case.

how does a polarizer work

The result is influenced by the angle between the camera's position and the reflecting surface. If the camera is at a low level to the reflection, the filter effect will be small. From a higher viewpoint, the effect will be much greater.
This is an effect that cannot be replicated in Photoshop.

Note
Polarizing filters will not work on bare metal.

How a polarizing filter works

Light travels in waves in all directions and at varying frequencies and sizes. The colour of the light is determined by the wave frequencies, while the brightness of the light is determined by the size of the waves.

When the filter is rotated it works like a grill, letting through waves of light in one plane, while blocking out other waves of light moving in different planes.

If the intention is to remove reflections from the surface of water, and the filter is rotated, this grill is in the position of vertical lines, letting only vertical light waves get through. All other light waves, including the horizontal waves from the reflections are blocked, hence no reflections.

The filter will work on skies the same way. It removes reflections from the very small water particles in the atmosphere, thus increasing the colour saturation and darkens the blue sky.

Note
Polarizers have a density of 1.3 stops which means exposure has to be increased by this amount. In low light levels, this can make hand-held photography difficult. Consequently, it is not going to be convenient or necessary to be using a polarizer all the time. Save it for when circumstances justify it.

Types of filters

Most are screw-in filters. Cokin filters are square and are made to fit their own holders and the holder rotates.

Polarizing filters can be either linear or circular. Linear polarizers give a stronger result but can upset metering systems and auto-focusing. These systems use surface-silvered mirrors in their operations and linear filters intefere with this. Linear polarizers will work fine on manual cameras and plate cameras.

All automatic cameras will require a circular polarizing filter.

Pros

Richer blue skies.
Reduced reflections on water and other surfaces except bare metal.
Richer greens with foliage.
Slighter more saturated colours.

Cons

The loss of 1.3 stops in exposure.
Sometimes the result on the sky can be too strong for a normal realistic effect, but this can be controlled by the degree of rotation.
Watch out for vignetting (darkening in the corners) when used with very wide lenses. More expensive samples with thinner glass can overcome this.
Not to be used on landscape panoramas because each image will have a sky of different densities and it won't be possible to blend everything in.

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