Abstract: An optical system (3) for transferring light energy from a light source (1), in particular a moving light source, to a common aperture independent of the location of the light source within a field of view, wherein the light energy distribution is preferably substantially uniform over the area of the common aperture. A detection system comprises a light source 1 for irradiating a spot on a moving object 0, an optical probe assembly 3 for collecting light energy from the irradiated spot on the subject 0 when within a field of view of the probe assembly 3, and a photodetector 4.