The invention relates to a small-format exposure head wherein ball lenses are positioned in alignment with individual devices of an organic EL array to efficiently collect a light beam from each device onto an image carrier such as a photosensitive material with no crosstalk yet with sufficient resolving power, and an imaging system incorporating the same. An array of organic EL devices is provided on a long length of substrate 3 in at least one row of pixel arrangement. On the light-emitting side of the array of organic EL devices, a ball lens 10 is positioned in alignment and contact with each light emitter 2 of the organic EL device. The ball lens 10 formed of a transparent material having a refractive index of 2 or greater.