Cokin A21 Dark Blue Conversion/Cooling Filter (80B) A-Series camera filter

Purpose & User

The Cokin A21 Dark Blue Conversion/Cooling Filter (80B) is a rectangular camera filter made for photographers using daylight-balanced film under tungsten or halogen lighting. It belongs to the A-Series system, which lets users stack or swap filters quickly without tools. The single-coated blue glass suppresses strong orange tones from artificial light sources while preserving the original colour balance of the scene.

Filter Factor & Wratten Rating

The filter carries an 80B designation, the single specification that tells you how much cooling correction it applies to tungsten light. This rating matches the needs of standard daylight film in typical indoor or street-lit environments. The A-Series mount ensures it fits the same holder as the medium blue A021 and light blue A022 filters for combined use.

Sustained Shooting Behaviour

Under continuous use the single-coated glass resists flare and ghosting when bright point lights such as party bulbs or illuminated monuments fill the frame. Shadows retain sculptured depth without turning muddy, and the coating cleans easily between long sessions. The rectangular shape covers wide-angle lenses without vignetting when mounted in the A-Series holder.