Kenko Moose's Warm 81A Circular Polariser Camera Lens Filter
Collaboration between respected wildlife photographer and conservationist B. Moose Peterson of Wildlife Research Photography and THK Photo Products, Inc., has created a circular polarising filter that uses 81A optical glass made by Hoya, the world's largest optical glass manufacturer, instead of the clear optical glass of a normal circular polarizer.
When using a camera with a split beam metering system (a metering system that employs a polarised half mirror) which is most of today's auto focus camera bodies, traditional linear polarizers will cause exposure errors due to their light absorption properties. Circular polarizers yield the same optical effect while not causing exposure problems with modern metering systems. For many years, polarizers have been used to remove reflections from non-metallic surfaces such as water and glass as well as being used to darken blue skies to increase contrast in scenic photography.
A side effect of both linear and circular polariser is they cool down or make the overall colour balance of a scene slightly bluish. The addition of the 81A glass corrects the colour temperature, bringing the scene back to the original 5500K for daylight film's colour balance. The 81A glass creates a much more pleasing and warm colour balance to the entire scene while the circular polarizer increases colour contrast and reduces the effect of atmospheric haze.