Absorbance, turbidimetric, fluorescence and nephelometric photometer

In a multi-function photometer having a sample cell for containing a liquid to be measured, a grating, an array of photodiodes, and a source of radiation directed along a first axis through the cell to the grating for dispersing the radiation according to wavelength onto respective different ones of the photodiodes, thereby to provide output signals corresponding to the intensity of radiation at each wavelength, the improvement wherein the sample cell defines an exit aperture perpendicular to the first axis, the exit aperture being positioned to be the entrance aperture for the grating.