Described are imaging systems that employ diffractive structures as focusing optics optimized to detect visual edges (e.g., slits or bars). The diffractive structures produce edge responses that are relatively insensitive to wavelength, and can thus be used to precisely measure edge position for panchromatic sources over a wide angle of view. Simple image processing can improve measurement precision. Field-angle measurements can be made without the aid of lenses, or the concomitant cost, bulk, and complexity.