ABSTRACT We present a concept for an X-ray imaging system with a high angular resolution and moderate sensitivity. In this concept, a two-dimensional detector, i.e., an imager, is put at a slightly out-of-focus position of the focusing mirror, rather than just at the mirror focus, as in the standard optics, to capture miniature images of objects. In addition, a set of multi-grid masks (or a modulation collimator) is installed in front of the telescope. We find that the masks work as a coded aperture camera and that they boost the angular resolution of the focusing optics. The major advantage of this concept is that a much better angular resolution, having an order of 2–3 or more than in the conventional optics, is achievable, while a high throughput (large effective area) is maintained, which is crucial in photon-limited high-energy astronomy, because any type of mirrors, including lightweight reflective mirrors, can be employed in our concept. If the signal-to-noise ratio is sufficiently high, we estimate that angular resolutions at the diffraction limit of 4″ and 0.″4 at ∼7 keV can be achieved with a pair of masks at distances of 1 m and 100 m, respectively.