The 81 Series of filters control the bluish coloration that affects daylight film. The stronger 81B warms scenes shot on overcast days more than an 81A. It can also remove more excessive blue from the effects of electronic flash. Good for general scenics when the photographer wishes to remove the bluish cast from open shade or add even more warmth to the photograph than with an 81A.
Specific for the Tamron 500 f8 mirror lens with 30.5mm rear filters.