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Polarizing Filter Effect

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If you want concentrate in Landscape Photography, don’t forget to have Circular Polarizer Filter. This filter is a “hand-book” of landscaper.

copied from Wikimedia, it says that Circular Polarization is :

The concept of circular polarization is similar to that to linear polarization. Circular polarization is a combination of two perpendicular linear waves that are 90 degrees out of phase with each other.

Example picture using HOYA CPL Filter :

Taken with Canon EOS 1000D + Lenskit 18-55mm

Location : Tulungagung

As any light wave can be represented as a sum of two linearly polarized waves, it also can be sought of as a sum of two circularly polarized waves, one rotating clockwise and another – counterclockwise. In physics, the circular polarizing filter is a device which when illuminated by wave containing both clockwise and counterclockwise components, would pass only one of them.

The ‘circular polarizer’ term when applied to filters used with modern photo cameras is misleading, because it does not do what is described above, namely, allowing to pass only one circular polarization. Which is good, because it is not what is required in this case. The circularly polarizing filter in photography consists of two components: first light passes though a regular linearly polarizing filter which allows only one linear polarization to pass and blocks another, and then light goes through a second component – a quarter wave plate which converts the linearly polarized light into a circularly polarized.

The first component allows to block or highly reduce light scattered from a sky at 90 deg. and reflections from shiny surfaces such as glass or water. The second component is needed for most of the modern cameras to work with the resulting light correctly. If your camera uses beam-splitter reflecting all or part of light at 90 deg. into auto-focusing device and into an exposure-metering system (e.g. if you have am SLR or DSLR camera), then it utilizes only one linear polarization out of incoming light. Both systems are designed to work with light which is not linearly polarized. However, if we place a linear polarizer in front of a camera, this light might be totally blocked by 90-deg reflection, and both exposure meter and auto focus will not work properly. So, to make the camera work after passing the light through a linear polarizer, we need to convert this light into a state which contains both linear polarizations in equal amounts. This is done with the use of a quarter-wave plate, which produces a circular polarized beam, which allows your SLR camera to function properly.


Written by Dimas A. Nugroho

February 26, 2010 at 5:49 am

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