A metrology apparatus for determining a characteristic of interest of a structure on a substrate, the structure having diffractive properties, the apparatus comprising: focusing optics configured to focus illumination radiation comprising a plurality of wavelengths onto the structure; a first detector configured to detect at least part of the illumination radiation which has been diffracted from the structure; and additional optics configured to produce, on at least a portion of the first detector, a wavelength-dependent spatial distribution of different wavelengths of the illumination radiation which has been diffracted from the structure, wherein the first detector is arranged to detect at least a non-zero diffraction order of the illumination radiation which has been diffracted from the structure.