Sigma 86mm EX DG, Digitally Optimized, Circular Polarizer Wide Angle Multi-Coated Glass Filter.

Digitally Optimized (DG) Filters
Ex DG filters benefit from Sigma's multi-layer lens coating, developed to counteract the highly reflective characteristic of image sensors. With older style filters, light would reflect off the image sensor, bounce off the lens and filter elements and re-enter the image sensor, creating a ghost image. The multi-layer coating dramatically reduces this effect. In addition to this, an optimum, neutral colour balance is ensured, increasing the white balance accuracy of the digital camera.

Circular Polarizing Filter
This type of Polarizing filter has a large diameter and it also deepens the intensity of blue skies, eliminates glare. It not only reduces the reflection from non-metallic surfaces, but also increases colour saturation perfectly