The classic use for a polariser is darkening blue skies, but they can also reduce reflections and increase theoverall colour saturation of your shots. The effect of a polariser varies as you rotate the filter, so most versions are circular and come in a mount that allows you to move the filter once it is fitted to the lens.

Lee Filters produces a square polariser for its filter system, but the more useful type is a screw-in version that attaches to the front of the Lee Filters holder using a 105mm adapter ring.Although almost all polarisers are circular in shape, they actually come in two types that are confusingly called linear and circular. This name describes the way that the filters work, rather than their shape, and which type you need depends on your camera. If your camera has autofocus or spot (or multi-segment) metering you need to use a circular polariser.

For older manual models you can use the cheaper linear type, although you can also use the circular type and the effect is the same. So, if you use a digital SLR make sure you're using a circular polariser to ensure that your camera will work properly!Knowing how these filters work relies on a little knowledge about how light behaves, so here comes the science bit. Normal light behaves like a wave, but vibrates in all directions. But some light - such as blue skies or reflections from non-metallic objects - is polarised, so that the waves all vibrate on the same plane.

A polariser works by only letting through light vibrating in a particular plane, so you can either block polarised light from reaching the sensor or let it through. A polarising filter can be rotated independently of the lens to control which light passes through and which is blocked. This can be tricky to see through the camera, but move the filter slowly and look out for blue skies darkening and lightening as you go. How you position the filter is down to personal preference, although there are some problems to watch out for that we'll cover later on.Are they just for blue skies? No!Although darkening blue skies is the most common use for polarisers, they are also great for removing reflections from non-metallic subjects and also increasing overall colour saturation.

For landscapes the ability to 'see' through water by removing reflections is handy, although you need to position the polariser carefully if you still want to darken the sky.A polariser can also be used as a makeshift overall neutral density filter, as they also reduce the amount of light reaching the sensor. This will allow you to use slower shutter speeds or wider apertures than without the filter in place, although the amount of light reduction will vary between 1 and 3 stops depending on the position of the filter and the amount of polarised light from the subject.While the effect of a polariser is useful for many shots, there are also times when hey either have little effect on the image or the result can look unnatural. As we've already mentioned, they also reduce the amount of light reaching the sensor, so in low light you will find that the shutter speeds will be too long to handhold the camera, or you have to use a wider aperture than you want.

As the amount of polarised light in blue skies varies depending on both the position of the sun and the amount of pollution in the air, the effect of a polariser can lead to some unwanted results. The most common when using wide-angle lenses is an uneven effect across the frame. Blue sky is most polarised at right angles to the position of the sun. So if it is a clear day and your shot includes a wide area of sky you can find that using a polariser will make the area at 90 degrees to the sun much darker than those nearer or opposite it. This can make the sky look uneven and unnatural.

A similar effect can also happen when the sky is very clear, especially if you are shooting from a high hill or mountain as the light is so clear it can go almost black if you use a polariser! So avoid using them in these conditions.Looking for more Tutorials? Visit Your-Digital-Photography.com Today!