Sigma 67mm WR (Water Repellent) Circular Polarizer Filter

This filter can minimize unwanted reflections on shiny surfaces, make skies more rich in color and give clouds greater presence, and in general make many images in many different situations pop from the screen or page in more dramatic fashion. 

Circular polarizer filters thread onto the front of camera lenses, and feature a rotating ring to adjust the angle of the filter’s light-passing axis in relation to the light sources in the image. As the polarizer filter is rotated, you can visually see the effects through the viewfinder or LCD screen. When the angle of the polarizer is at maximum to the direction of the light, the effect will be most pronounced, as will the exposure impact. If you are in a program mode, you may notice the exposure values change and slow by a full stop or more. If you are in manual, you will notice the metering changing.