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The realization of X-ray telescopes with imaging capabilities in the hard (>10 keV) X-ray band requires the adoption of optics with shallow (< 0.25 deg)grazing angles to enhance the reflectivity of reflective coatings. On the otherhand, to obtain large collecting area, large mirror diameters (< 350 mm) arenecessary. This implies that mirrors with focal lengths >10 m shall be producedand tested. Full-illumination tests of such mirrors are usually performed withon- ground X-ray facilities, aimed at measuring their effective area and theangular resolution; however, they in general suffer from effects of the finitedistance of the X-ray source, e.g. a loss of effective area for doublereflection. These effects increase with the focal length of the mirror undertest; hence a "partial" full-illumination measurement might not be fullyrepresentative of the in-flight performances. Indeed, a pencil beam test can beadopted to overcome this shortcoming, because a sector at a time is exposed tothe X-ray flux, and the compensation of the beam divergence is achieved bytilting the optic. In this work we present the result of a hard X-ray testcampaign performed at the BL20B2 beamline of the SPring-8 synchrotron radiationfacility, aimed at characterizing the Point Spread Function (PSF) of amultilayer-coated Wolter-I mirror shell manufactured by Nickel electroforming.The mirror shell is a demonstrator for the NHXM hard X-ray imaging telescope(0.3 - 80 keV), with a predicted HEW (Half Energy Width) close to 20 arcsec. Weshow some reconstructed PSFs at monochromatic X-ray energies of 15 to 63 keV,and compare them with the PSFs computed from post-campaign metrology data,self-consistently treating profile and roughness data by means of a methodbased on the Fresnel diffraction theory. The modeling matches the measured PSFsaccurately.

Angular resolution measurements at SPring-8 of a hard X-ray optic for the New Hard X-ray Mission