An optical spectrometer apparatus (200") comprising a linear array detector for receiving light at a predefined range of wavelengths, arranged to record one or more first detection signals that represent relative light intensities at wavelengths within said predefined range of wavelengths; and a point detector (210d, 210f) for receiving light at a predefined wave-length that is outside said predefined range of wavelengths, arranged to record a second detection signal that represents relative light intensity at said predefined wavelength characterized in that the optical spectrometer apparatus comprises an arrangement of a collimating optical element, a diffracting optical element, and a focusing optical element that are arranged to provide at least a first optical path that guides incoming light at said predefined range of wavelengths to the linear array detector via the collimating optical element, the diffracting optical element and the focusing optical element such that light at said predefined range of wavelengths is forward diffracted from the diffracting optical element towards the focusing optical element, and a second optical path that guides incoming light at said predefined wavelength to the point detector (210d, 210f) via the collimating optical element, the diffracting optical element and the collimating optical element such that light at said predefined wavelength is back diffracted from the diffracting optical element towards the collimating optical element, wherein the collimating optical element also serves as the focusing optical element for light at said predefined wavelength. a linear array detector for receiving light at a predefined range of wavelengths, arranged to record one or more first detection signals that represent relative light intensities at wavelengths within said predefined range of wavelengths; and a point detector (210d, 210f) for receiving light at a predefined wave-length that is outside said predefined range of wavelengths, arranged to record a second detection signal that represents relative light intensity at said predefined wavelength characterized in that the optical spectrometer apparatus comprises an arrangement of a collimating optical element, a diffracting optical element, and a focusing optical element that are arranged to provide at least a first optical path that guides incoming light at said predefined range of wavelengths to the linear array detector via the collimating optical element, the diffracting optical element and the focusing optical element such that light at said predefined range of wavelengths is forward diffracted from the diffracting optical element towards the focusing optical element, and a second optical path that guides incoming light at said predefined wavelength to the point detector (210d, 210f) via the collimating optical element, the diffracting optical element and the collimating optical element such that light at said predefined wavelength is back diffracted from the diffracting optical element towards the collimating optical element, wherein the collimating optical element also serves as the focusing optical element for light at said predefined wavelength. a first optical path that guides incoming light at said predefined range of wavelengths to the linear array detector via the collimating optical element, the diffracting optical element and the focusing optical element such that light at said predefined range of wavelengths is forward diffracted from the diffracting optical element towards the focusing optical element, and a second optical path that guides incoming light at said predefined wavelength to the point detector (210d, 210f) via the collimating optical element, the diffracting optical element and the collimating optical element such that light at said predefined wavelength is back diffracted from the diffracting optical element towards the collimating optical element, wherein the collimating optical element also serves as the focusing optical element for light at said predefined wavelength.