Formatt Linear Polarizer 5.650" x 5.650" Filter CAT BF PXP-POLAR4

The linear polarizer is the standard polarizing filter, and is an essential outside all-purpose filter. The principal use of the polarizer is to eliminate surface reflections, glare and hot spots from any light source entering the camera. This reflected light often shows up as a whitish glare which reduces the color in the image. The polariser is used for color and contrast enhancement and removes reflections from substances such as water and glass. For example polarizer filters can darken a blue sky and increases color saturation.

Pol filters are typically rotated to achieve the required effect; for this purpose you should ensure that your matte box has at least one rotating filter tray.

When two polarizers are placed together it is possible to achieve near black out, dependent on the angle in which they are aligned. This enables intense effects to be created. One of the polarizers is rotated until the required effect is achieved.

After a clear protection filter, a polarizer is probably the first filter which any camera user should purchase.

Polarization:
Natural daylight is partially polarized. When light from the sun hits molecules in the atmosphere, the blue end of the spectrum (the short wavelengths) is significantly scattered. This scattered light is partially polarized. The red end of the spectrum is largely unscattered and consequently less polarized. The resulting light reaches the surface of the earth from all directions and makes the sky appear bright and blue. Without an atmosphere the sky would appear black.

Use of Formatt polarizing filters can remove the scattered (and partially polarized) component of the light and only allow light in one plane to pass. The effect of this is to darken clear skies. Where there is moisture present, mist, haze, smoke etc, the scattered light appears white owing to the large size of the molecules. These larger molecules have a de-polarising effect. Consequently using a Formatt polarizer will significantly increase the contrast between clouds and sky.

From Malus's Law the maximum level of light which can pass through a polarizer is 50%. Formatt filters are HN38 polarizers, meaning that a maximum of 38% can pass. This equates to 1 1/3 stops and suitable adjustments should be made. Formatt uses a very high specification iodine tinted polymer for its polarizers, ensuring a neutral grey with a flat transmission curve, minimising the risk of any colour distortion.

Extinction values on crossed Formatt Polarizers are better than 98%.

CAT BF PXP-POLAR4