A polarizing filter is just one type of filter that can be attached to lenses.
Polarized lenses are lenses that have a polarizing filter attached to them. These filters eliminate light rays of a certain orientation and typically deepen colors, enhance contrast and allow you to view through certain transparent surfaces, such as water. However, some problems can occur when using a polarized lens. These problems may occur infrequently, but they can be annoying if they occur.
Uneven Polarization
Polarizing lenses deepen blue skies in photographs, but may do so unevenly. The sky is subject to natural polarization, and using a polarizing filter may not eliminate light rays evenly from different areas across the sky. This effect is most common when facing 90 degrees away from the sun and at high altitudes. At its most extreme, one area of the sky will be blue while the opposite area may appear almost black, which can be undesirable.
Low-Quality Glass
Lens filters, at their core, are simply an additional glass element you place in front of a lens. This means they are subject to the same issues as lens glass: scratches, dust, sharpness, blurring, etc. If you have a poorly manufactured or damaged filter, the resulting image will be subject to those impurities.
Vignetting
Occasionally, a lens filter may cause vignetting, which is the darkening of an image's edges in a circular manner. This effect is caused by the edges of glass elements that are not transmitting as much light at other regions. It is most frequently seen with wide-angle lenses and when multiple filters are attached. This effect is typically undesirable, since a vignette can be added digitally later.
Unexpected Polarization
Finally, a problem you may encounter with polarized lenses is the unexpected polarization of some objects. All objects are subject to polarization to some extent, while some, especially those that are capable of glare, are highly reactive. The result may be an unnatural-looking image due to the tone difference. Cell phones and laptops screens are particularly effected by filters since they emit light in only one orientation.
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