A detection system for detecting luminescence sites on a substrate and including an irradiation unit for generating at least one excitation irradiation beam for exciting luminescence sites on the substrate; a first optical element, e.g. refractive element adapted for receiving at least two irradiation beams of different wavelengths or wavelength ranges, the at least two irradiation beams being excitation irradiation beam(s) to be focused on a substrate and/or luminescence irradiation beam(s) to be collected from the excited luminescence sites on the substrate; and an optical compensator for adjusting at least one of the at least two irradiation beams of different wavelengths or wavelength ranges so as to reduce or compensate for optical aberrations.