Polariser filter

From MyOlympus

Questions

Q: When is it beneficial to use a polarizing filter on my camera?

Q: I have problems seeing the effect of the polarizing filter. Any tips?

Answers

Q: When is it beneficial to use a polarizing filter on my camera?

A: If a polarizing filter is rotated to the correct angle, it will reduce light reflections from wet surfaces, asphalt, glass etc. or darken the blue sky but leaving the white clouds essentially bright. You also use it to reduce haze and glare in misty or polluted air conditions. You can use it all the time but it will steal about 1-2 f-stops of light and it will not have any noticeable effect in other situations than the above mentioned.

• A polariser filter helps to obtain deep blue skies and to remove unwanted reflections. The polariser filter substantially reduces the amount of light reflected by the water surface making the sea ground more visible and makes the sky more dark.
• Polariser filters are also useful when the lower part of the image is dark and the top (the sky) too bright.
• Have a look at Darwin Wigget's page on filters for further information on polariser, blue-yellow polariser, graduated neutral density and other filters
• See also Jeremy McCreary's page on filters

For a deeper explanation see [1]

The effect of using circular polarising filters versus linear ones is not clear. Olympus states that "A 58mm circular polarizer is recommended. Linear polarizers cannot be used. Linear polarizers will effect image exposure and auto focus." with respect to the C-8080. Here are possible reasons

• Linear and circular polarizers both consist of a linear polarizer foil but differ in their construction in the following way. Modern SLR cameras have have a beam-splitting prism that sends part of the incoming light to the meter and part to the viewfinder. The effect is that the light entering the meter is partially polarized by the beam-splitter. A linear polarized placed on the lens of such a system will act as a second polarizer and block light to the meter by a degree dependent on the angle between the prism and the polarizer on the lens. The result is incorrect exposure/aperture values from the meter. The circular polarizer circumvents this problem through the addition of a 1/4-wave retarder, or delay, foil. This ensures that the linearly polarized light is changed into a rotation that appears unpolarized to the meter, resulting in proper exposure/aperture readings. (cited from [2])
• "Wide angle lenses do polarize light on their own to a large extent." [3]

On the other hand there are reports about successful uses of linear polarising filters in some models (eg. 8080 - which is no SLR).

Q: I have problems seeing the effect of the polarizing filter. Any tips?

A: The following might help:

• The preview on the LCD monitor of your camera adjusts automatically to the brightness of the framed subject. This might compensate the effect when you turn your polarising filter. You can try to use the Auto Exposure Lock AEL of your camera. This should prevent the display from compensating.
• The strength of the effect of a polarizing filter depends on the angles between the sun, your camera and your subject. A good starting point is to turn the polarzing filter so that the knob on the moving ring points to the sun.