Light which falls on electrically insulating surfaces, e.g. glass, plastic, glossy lacquer or water*, at an angle (not perpendiculer) is polarized by reflection to an extent that depends on the angle of incidence. Consequently, its waves do not oscillate in all directions, but mainly or exclusively on a “polarization plane”. Therefore polarizing filters or shorter polarizers permit weakening, complete elimination, but also enhancing of reflections. A blue sky can be colored more intensively and the color saturation of landscapes can be enhanced by eliminating the bluish veil. The effect of these filters cannot be replaced by a digital imaging software at a later date.

* The electrical conductivity of water is too small for avoiding polarization.

Polarizing filters have a polarizing film between two protecting glass plates inside a rotating mount, which is transparent only for light oscillating on a specific plane. Depending on the orientation of the filter, polarized light is rejected completely or partially. Just as with a Neutral Density Filter ND 2x, normal un-polarized light (= mixed polarized) is darkened at a rate of about 50 %. Apparently more light-transmissive polarizing filters can achieve this effect only at the cost of less polarization! This means that the gain in transmission is achieved at the cost of the desired effect.

Circular Polarizing Filters are applicable for all cameras, even for those with a beam splitter in front of the AF-sensor or for a TTL light meter cell (where linear polarizing filters cannot be used). The HR Digital Circular Polarizing Filter is characterized by the following features:

• Due to a 7 layer multi-coating the transmission of light is especially high and reflection very low. Therefore double images and stray light can be avoided even better.
• An extra protection layer which is extremely scratch-proof, water-repellent and dirt-resistant makes the glass plates robuster. This layer does not have any influence on transmission, it keeps the surface clean for a longer time and allows easy cleaning.
• Due to its minimal heat extension even for heavy variations in temperature, the brass mount does not create any quality-reducing mechanical tensions in the filter glass. Furthermore, the danger of getting stuck in the filter thread of the lens is reduced by the high slide capacity of brass.

The HR Digital Circular Polarizing Filter is available with a slimline mount in sizes from 49 mm to 82 mm. It is fitted with a female thread at the front side and a male thread of the same size at the rear. So an additional filter or a lens hood can be fixed.