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Article 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
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 (1781–1868). 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.
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