Colour compensating filters control colour by attenuating principally the red, green, or blue part of the spectrum. They can be used to make slight changes in the colour balance of images recorded on colour films, or compensate for deficiencies in the spectral quality of a light source. These filters will work perfectly with colour temperature meters where even slight variances of colour will cause a problem. For shorter focal lengths 20-24 or 28mm as well as for wide-angle zooms (24-50mm, 28-85mm, 35-135mm) System P is strongly recommended. It is available in diameters ranging from 48 to 82mm & eliminates vignetting.