 BetterPhoto Member |
Restrictions On Polarizing Filters? Hi! What are the restrictions on using polarizing filters? Certain angles? Thank you,
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Jeff S. Kennedy |
I'm not aware of any restrictions or laws against polarizing filters. ;-))) Seriously, polarizers are most effective when used at 90 degrees to the sun. They also will remove glare from water and glass but not from metalic objects.
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John A. Lind |
Jeff's right about polarizers having greatest effect on northern and southern skies, but little to none with eastern or western skies. As Jeff mentions, polarizers can also be used to remove glare from non-conductive (non-metallic) surfaces. However, just as with sky, maximum effect is achieved when the lens axis is at a specific angle to the glare surface. This angle is called "Brewster's Angle" and is the angle at which the greatest amount reflected light is polarized by the reflection. The exact angle for a specific material is based on the index of refraction for the material (e.g. glass, water, etc.) and the index of refraction for air (presuming the reflective object is in air and you're not doing underwater photos): Theta = Arctan( n2 / n1 ) A polarizer will have near zero effect on glare reduction if the lens axis is at 90 degrees (perpendicular, or normal) to a surface. The effect increases until Brewster's Angle is reached, and then decreases again. For practical photography, Brewster's Angle is usually between 30 and 60 degrees. For water in particular, it's approximately 50 degrees. -- John
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Kerry Drager |
Hi Tracey: Some excellent advice from Jeff and John! Just a few more thoughts: - Be sure you have a precise reason for using the polarizer. For instance: If the sky is already a deep blue, the addition of the polarizer could turn that rich-blue sky almost black. Also, if you like the sparkles in a water scene, you might not want to tone it down with a polarizer. However, if the colors in a scene seem subdued, you might want to try a polarizer in order to remove possible glare and beef up the colors. - Beware when using a wide-angle lens in a horizontal format. Since this filter works at an angle to the sun, the result of trying to capture such a broad sweep of sky with a polarizer could result in an uneven, unnatural effect - i.e., a sky that's deep blue at one side of the picture frame while gradually turning to a pale blue at the other. - Remember: You can preview a polarizer's possible impact by holding it up to your eye, rotating it, and (hopefully) telling whether you'll need to use it. - Sometimes I simply can't tell whether a polarizer will help (or hinder) a scene. In those cases (and assuming my subject sits still long enough), I'll shoot two frames of the scene - both with AND without the polarizer - and then compare the results later. Hope this helps! Kerry
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Jeff S. Kennedy |
Another thing to remember is that it doesn't have to be a sunny day to use a polarizer. On overcast days a polarizer works to remove glare from foliage. The result is more saturated colors. A polarizer can also be used in place of or in addition to a neutral density filter to reduce the amount of light. This allows you to open your lens up more to shorten DOF or lets you slow your shutter speed down to impart motion in your shots (ie. silky waterfall shots).
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