Redrock microFilter Circular Polarizer — a 4×5.65 circular polarizing filter. A polarizer is one of the first filters needed for outdoor shooting. Its primary use is removing unwanted glare and reflections from non-metallic surfaces, reducing flare from any light sources in the frame, and darkening the sky while increasing saturation. It also improves color and contrast and removes reflections from water and glass. The effect can be seen through the viewfinder and adjusted relative to the sun by rotating the filter.
In addition to the polarizer, a circular polarizer includes a quarter-wave plate that converts linearly polarized light into circularly polarized light. In terms of the visible effect in the frame, it does not differ from the common linear polarizer. However, circularly polarized light does not interfere with phase-detection autofocus systems in DSLR cameras and does not complicate metering.