An electron beam imaging system (10) includes a photoemitter plate (12). An optical image beam (15) is directed through a pattern mask (18), which is imaged onto the photoemitter (12). The photoemitter (12) emits electrons from those unmasked regions illuminated by the optical image beam, emitting an extended-source electron beam that carries the mask image. The extended-source electron beam is focused (34) onto a device under fabrication (40), providing a single-stage electron lithographic patterning function. The optical source (16) is chosen so that optical image beam energy is nearly identical to the work function for the photoemissive coating (14) of the photoemitter (12). As a result, the photoemitter (12) emits electrons with substantially zero kinetic energy, allowing the emitted electrons to be accelerated through the electron beam focusing elements (34) with very nearly identical electron velocities, thereby minimizing chromatic aberrations. In one embodiment, an aperture (85) is used to limit the extended-source electron beam to those electrons with trajectories requiring no more than a maximum amount of focusing, thereby minimizing spherical aberrations.