Optical multi-channel measurement unit for a process measurement includes first ends for receiving optical radiation from the optical radiation source, and second ends for outputting the optical radiation for illuminating the at least one object. Optical detectors receive optical radiation from at least one measurement channel via at least one optical filter and convert an intensity of the optical radiation to an electrical signal. A movement mechanism causes, for filtering the wavelengths of the optical radiation propagating between detectors and the optical measurement channels through the optical filters, at least one of the following: movement inside at least one optical filter and movement between the filters and the detectors.