B&W Bay 6 CC40Y (Yellow) Color Compensating (Color Correction) filters act specifically on relatively narrow bands of color. That is why they do not come in two color variants (bluish and reddish) like conversion filters do. Instead, they come in three primary additive colors and their three secondary colors (which can be interpreted as the primary colors of subtractive mixing) - each color comes in practical density steps.
B&W Color-Cast-Correction or CC filters distinguish themselves from gelatin or acetate foils, in that gel or acetate filters must be inserted in filter holders. B&W CC filters consist of high-grade but very sensitive original Kodak foils cemented between precisely fabricated plano-parallel optical glass discs that are edge-sealed for protection against humidity and immune from finger prints, scratches and dirt.
Some photographic situations require specific color corrections. For example, when shooting daylight film under fluorescent lighting, some magenta correction is needed in order to remove the greenish tint that would otherwise appear. The amount of color correction required is most accurately measured via a color temperature meter.
This filter is specific to lenses with Rollei's exclusive Bay 6 filter size.