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Polarizer's

A flowing river with reflection enhanced with a polarizer

A circular polarizer is a filter that can be fitted either to the front of a lens, screwing into the filter thread or can be a part of a filter system fitting into a filter holder. The filter has a rotating part allowing the filter to be at different angles, producing different effects. It has a number of uses and is probably the most widely used filter next to a protective filter used by photographers.

Polarizers are available from a range of manufacturers, and price increases with size. Hoya prices for a 52mm is 24.40, going up to 93.50 for a 86mm. A 77mm, my largest lens, would cost 59.60, while the Cokin circular polarizer to fit the 84mm P system I can use with this lens cost 49.90. See also filter holders and systems

Rather than have a polarizer for each lens, you can have one for your largest size and then use stepping rings to fit this to smaller lenses, or of course use a filter holder based system.

Polarizer's have several uses:-

  • Used at about right angles to the sun they make sky's bluer and white clouds show out as well as saturating colours.
  • They can increase reflections, such as in water or windows.
  • You can reduce or eliminate reflections.
  • You can see through the surface of water so, for example seeing fishes more clearly.
  • You can often reduce mist or haze, and often make longer shots clearer.
  • You can often get colours to show better.

The different effects are obtained by rotating the filter, so in one direction reflections are increased, while through 90 degrees they are reduced. Other effects are related to the direction of the sun and the angle you are to a surface, such as water or glass.

Clouds and blue sky enhanced with a polarizer.

The effect on reflections is explained by a mathematical theory known as Brewster's angle (also known as the polarization angle) after the Scottish physicist, Sir David Brewster (17811868). This is also used in polarized sunglasses to cut glare. With reflections etc, there is an optimum angle at which this works. With air into water this is around 53 degrees down from vertical or 37 degrees up from the ground. This is often about the ideal angle when looking for reflections in lakes and water generally, or seeing through the surface. It works a long way outside this ideal, and perhaps we only need to know about this on the occasions we can't get the results we want and changing our angle may help.

Some light goes from the sun, reflects on the item you can see and to you, other light is scattered by clouds, by water and a variety of other means, some of the effect is obtained by eliminating this scattered light.

Left - Cokin P Polarizing filter and Right - 77mm screw-on polarizing filter


See also: Filter Section for more articles.

 


By: Keith Park Section: Filter Section Key:
Page Ref: polarisers Topic: Filters  Last Updated: 05/2009
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