Cokin A709 Cyan Color Correction Filter CC09C A-Series

System A for lenses between 36 and 62mm in diameter is recommended for focal length over 35mm.
Color Compensating Filters - Control color by attenuating principally the red, green, or blue part of the spectrum. They can be used to make slight changes in the color balance of images recorded on color films, or compensate for deficiencies in the spectral quality of a light source. These filters will work perfectly with color temperature meters where even slight variances of color will cause a problem.