X-ray optics: a technique for high resolution imaging.

Both scattering and figure errors in grazing incidence optics are larger in the plane of incidence than out-of-plane by a factor equal to 1/sintheta, where theta is the graze angle. When the full annular aperture of a grazing incidence telescope is stopped down, the point spread function becomes highly elliptical with a width as much as sintheta times narrower than the full image. In practice this means that improvements in resolution of up to 100 times can be achieved, and effective resolution can approach the diffraction limit. Laboratory data demonstrating the effect are presented.