1. A device in which an ultra-fine- focus x-ray tube or electron gun produces an electron beam focused to an extremely small image on a transmission-type x-ray target that serves as a vacuum seal; the magnification is by projection; specimens being examined can thus be in air, as also can the photographic film that records the magnified image.

2. Any of several instruments which utilize x-radiation for chemical analysis and for magnification of 100-1000 diameters; it is based on contact or projection microradiography, reflection x-ray microscopy, or x-ray image spectrography.