WISE results for a Wolter-I mirror, λ = 20 Å, with the dimensions listed in Fig. 11 and the same kind of error, but now w₁ = − 30 arcsec, w₂ = + 20 arcsec. The PSF computed from Eqs. (41) and (46) now has a pronounced asymmetry, confirmed by the ray-tracing findings (dashes). The detector resolution is 50 μm. In contrast, the single-reflection PSF computed assuming a profile error according to Eq. (50) with w₁ = − 10 arcsec would return a completely incorrect picture (blue line).