An objective colour L projects the image of a point source W along a continuum of monochromatic images located on the optical axis ("colour coding").
A sample placed in the area of colour coding shows the surface diffuse the incident light brush.
Backscattered light through the lens colour L in the opposite direction and arrives at a hole P that filters all wavelengths except one, λM.
The collected light is analyzed by a spectrograph S. The position of the sample is directly related to the wavelength detected λM.