The acuity of compound eyes is determined by interommatidial angles, optical quality, and rhabdom dimensions. It is also affected by light levels and speed of movement. In insects, interommatidial angles vary from tens of degrees in Apterygota, to as little as 0.24 degrees in dragonflies. Resolution better than this is not attainable in compound eyes of realistic size. The smaller the interommatidial angle the greater the distance at which objects--prey, predators, or foliage--can be resolved. Insects with different lifestyles have contrasting patterns of interommatidial angle distribution, related to forward flight, capture on the wing, and predation on horizontal surfaces.