This paper reviews the formation of an image with coherent and incoherent radiation. It discusses the various mm-wave methods for electronic beam-forming and beam-steering such as phased array, leaky-wave antennas, up-conversion, tapped delay lines and digital beam-forming techniques. These methods are related in the paper to their optical analogues of beam-forming and steering by a lens and the measurement of the aperture function in the case of holography. It concludes that digital techniques will be used in the future when the cost of receivers is reduced but that at present opto-mechanical techniques are more cost effective. A high efficiency, compact opto-mechanical system is described. This is able to operate at any wavelength and be active or passive. Typical 94GHz images are presented.