I am a landscape photographer and since in such photography the lighting conditions are rarely, if ever, ideal some adjustment is usually called for. One of the tools that I have found ideal for this purpose is Singh-Ray Blue and Gold Polarizer. I now own five of these polarizers for my different lenses.
Blue and Gold polarizer adds a level of color performance to my photos which I am unable to obtain with any other polarizer. A polarizer operates predominantly on reflected light and the Blue and Gold can be used to selectively give the reflected light a golden or bluish hue and its degree can be controlled by turning the polarizer. This effect can not be achieved by changing the color temperature alone in post processing since that will give the desired hue to the entire picture.
The attached picture shows the golden hue achieved on the ocean water at a beach in California that has a whale shaped rock, an unusual feature indeed.
Also, I have not observed any degradation in the sharpness of my pictures when using this polarizer, a testimony to the high quality glass used in its manufacture.
I strongly recommend this polarizer for landscape photographers.
It is a quality US made product. Five stars indeed.