A reduced footprint collimator device to focus light beam over length of optical path for use in an optical cytometry device or other optical instrument where a focused beam of light is passed through a test medium and then sampled by a photomultiplier or multiple photomultipliers for analysis. This device provides alignment and focus of that beam and collimation along the entire beam path. In addition in order to reduce the overall footprint of the beam path this device uses a precision coated prism to redirect the optical path perpendicular to the entering optical beam. The reduced footprint collimator device to focus light beam over length of optical path generally includes a reduced footprint 90 degree collimator which allows light beam collimation, beam path alignment, selectable beam focal distance, and reduces stray light reflections all in a minimal footprint.an These features allows for a smaller overall instrument design.