"82" series color corrective filters are light balancing filters used to increase the color temperature for a cooler (bluer) tone. They correct the tendency toward reddish tones and come in several strengths, A, B, & C, with A being the mildest effect.There are five filters available in two sizes. The Biogon 28, Planar 35, Planar 45 and the Sonnar 90 require the 46mm size, while the Biogon 21 requires the larger 55mm size. The five filters available in both sizes are: Contax Protective filter (P), Contax Multi-Coated Ultra-violet (L39) (UV), Contax Multi-Coated Skylight (1A), Contax Multi-Coated A2 (Warming) Filter (81B), Contax Multi-Coated B2 (Cooling) Filter (82A).