Microstructures can be viewed as nonimaging devices where all edge rays involved do not change direction over the aperture(s) of the device. This is equivalent to saying that the distance to source and target is much larger than the dimension of the device, which justifies the name microstructure for these devices. Consequently the shape of a microstructure device is independent of its size in this limit. The condition that the etendue of source and target must be equal, generally implies that the projected angle and not the angle itself under which source and target are seen must be equal. This requires at least two surfaces (reflective or refractive). We show how the shape of these two surfaces can be simultaneously tailored to the desired 4 directions delimiting a finite source and target.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.