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Polarizing filters reduce the light passed through to the film or sensor by about one to three stops (2–8×) depending on how much of the light is polarized at the filter angle selected. Auto-exposure cameras will adjust for this by widening the aperture, lengthening the time the shutter is open, and/or increasing the ASA/ISO speed of the camera.
If light entering the camera is already linearly polarized, it can upset the exposure or autofocus systems. Circular polarizing filters cut out linearly polarized light and so can be used to darken skies, improve saturation and remove reflections, but the circular polarized light it passes does not impair through-the-lens systems. [13]
Reflections, especially from water and wet road surfaces, are partially polarized, and polarized sunglasses will block some of this reflected light, allowing an angler to better view below the surface of the water and better vision for a driver. Light from a clear blue sky is also polarized, and adjustable filters are used in colour photography ...
The emitted light and the reflected light combine and may be considerably more visible than the original light. The most visible frequencies are also those most rapidly attenuated in water, so the effect is for greatly increased colour contrast over a short range, until the longer wavelengths are attenuated by the water.
Uncoated filters can reflect up to 12% of the light, [30] single-coated filter can reduce this considerably, and multi-coated filters can allow up to 99.8% of the light to pass through (0.2% unwanted reflection); the loss of light is not important, but part of the light is reflected inside the camera, producing flare and reducing the contrast ...
On the other hand, it does remove s polarized light, increasing the round trip loss for that polarization, and ensuring the laser only oscillates in one linear polarization, as is usually desired. And many sealed-tube lasers (which do not even need windows) have a glass plate inserted within the tube at the Brewster angle, simply for the ...
Polarizing sheets are used in liquid-crystal displays, optical microscopes and sunglasses.Since Polaroid sheet is dichroic, it will absorb impinging light of one plane of polarization, so sunglasses will reduce the partially polarized light reflected from level surfaces such as windows and sheets of water, for example.
At any particular wavelength, partially polarized light can be statistically described as the superposition of a completely unpolarized component and a completely polarized one. [5]: 346–347 [6]: 330 One may then describe the light in terms of the degree of polarization and the parameters of the polarized component. That polarized component ...