The Heliopan 55mm Slim Circular Polarizer SH-PMC Filter helps to reduce reflections and glare by filtering out light that has become polarized due to reflection from a non-metallic surface. This results in a noticeable increase in the saturation of skies and foliage, as well as clearer imagery when photographing in hazy conditions. A circular polarizer differs from a linear polarizer in that it supports full use of a camera's autofocus and auto exposure functions. The filter is constructed using high quality Schott glass, which maintains optical clarity and contrast to help render scenes with greater fidelity and resolution. The SH-PMC multi-coating provides a total of 16 coatings, 8 per side, for significant reflection reduction (below 0.2%) as well as dust and moisture repellence for easier cleaning. This filter features a brass mounting ring that is demarcated with calibration dots to help with finding consistent rotational positioning when TTL viewing is not possible. The ring also features a slim mount design, measuring 5mm-thick, that helps to prevent vignetting when used on wide-angle lenses. It does not feature front threads for mounting additional filters or lens caps.