Polarisers for B/W and colour film, digicams, and camcorders
One of the most commonly used filters is a POLARISER. It has the unique ability to be able to subdue reflections from non-metallic surfaces such as glass or water, darkens blue skies and enriches colours, acts as a light neutral density filter, and absorbs ambient UV light. It is supplied in a rotating filter mount as it has to be turned on the lens to vary the effect. There are two types: linear and circular.
Linear Polarisers (not for autofocus cameras) are slightly better at subduing reflections than a circular polariser. If you put two linear polarisers together, and rotate one against the other, the amount of light passing through the combination will dramatically reduce. You can use two polarisers to make a fader or variable density filter. If you put crumpled cellophane, cling film, or clear thin stressed plastic between the two polarisers you will see a changing colour pattern as the filters are rotated against each other. To avoid operational problems with autofocus cameras and camcorders you will need to use a CIRCULAR polariser.
Circular Polarisers (for both manual and autofocus cameras)are slightly better than linear polarisers at darkening blue sky and enriching colours. Circular does not refer to the shape of the filter, but to the type of polarising material, which is sandwiched with a 1/4 wave plate to make the filter. Due to its construction, the filter can only be used one way round.
