Abstract: A flow cytometry apparatus includes a transparent liquid flow chamber and a nozzle for providing a stream of particles, to be analyzed, through the flow chamber. A light source is provided along with a lens for focusing the light from the source at a region within the flow chamber through which the particles pass and for collecting light associated with those particles. Photoreceptors and the like are provided for detecting one or more characteristics of the particles related to light which strikes the particles. A spring or like biasing member provides and maintains stability between the lens and the flow chamber to particularly stabilize the relative axial position of the flow chamber and the lens.