Abstract: An optical scanner is provided wherein each waveband, i.e. blue, green and red, is detected during successive revolutions of an analyzing drum. A variable scanning aperture disc selectively transmits a different image portion during each waveband scan so that the image portion detected during each waveband scan is transversely displaced along the axis of the analyzing drum. The transverse distance of optical image portion displacement corresponds to and corrects for the transverse distance travelled by the optical scanning head during one revolution of the analyzing drum. Magnification optics are also provided for, inter alia, adjusting the transverse displacement of the image portions.