Photographing the Milky Way

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Circular Polarizer Filter
sə́rkjələr póləràjzɪŋ fɪ́ltər

A circular polarizing filter is a photographic filter that is attached to a lens in order to cut down glare and reflections as well as darken a blue sky. Polarizers work by stopping light from passing through the lens randomly from any wave angle, and only allowing one polarized wavelength of light to pass through. Rotating a circular polarizer broadens or narrows the angle of "acceptable" light, effectively turning "off" or "on" the polarization effect on reflections and other shiny surfaces. Circular polarizing filters are often used in landscape and product photography, but can also be useful in any application where glare or reflections are a concern.

How A Circular Polarizer Works

A circular polarizing filter can do amazing things for both outdoor and indoor photographers, whether the subject is the natural world or something entirely man-made. The reason for this is how a polarizer works, and how light itself works at an atomic level.

A reflection is created by waves of light that are polarized in mostly one linear direction, instead of the infinitely random angles that light waves can travel travel at. A polarizing filter, because of its atomic structure, only allows light from one single polarization (angle) to pass through it, and if that angle does not match the angle of the reflected light, it is partially or almost fully blocked. (Being only faintly blocked if it is nearly the same angle, and nearly all blocked if the angle of polarization is 90 degrees different from the angle of the polarized light.

Circular Polarization versus Linear Polarization

In photography, a linear polarizer and circular polarizer have the same exact effect on your image, when they are both used at the correct angle for maximum polarization. However a circular polarizer filter also includes a second layer of material called a quarter-wave plate, which takes the linearly polarized light from the polarizing layer, and turns it into circularly polarized light.

This is necessary on most modern cameras because both autofocus and metering can utterly fail if they receive linearly polarized light.

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