An astronomical interferometer is an array of telescopes or mirror segments that act together to provide higher resolution by means of interferometry. By masking the all but a few, small, widely spaced segments of a telescope provides the same angular resolution of a complete instrument with the same aperture. The main drawback is that it does not collect as many photons as the complete instrument's mirror. Thus it is mainly useful for fine resolution of more luminous astronomical objects, such as close binary stars. Another drawback is that the maximum angular size of a detectable emission source is limited by the minimum gap between detectors in the collector array.