The pre-launch HRI positional resolution was measured in the lab using
a shadow mask with a test pattern consisting of alternating bars of
open and closed area of various widths, as shown in Figures 4.13 and
4.14 of Appendix F. Mean values from such measurements
gives
= 8.4
m, which at the ROSAT X-ray telescope
focal length of 2.4 m, yields an intrinsic FWHM resolution of
1.7'' for the HRI.
Large scale geometrical distortions of the HRI were measured by projecting a mesh
pattern on the face of the detector (cf. Appendix F and its Figure
4.15 for details) and found to be less than 1'' over its
field of view. Note, however, that the image resolution varies over
the field due to the off-axis response of the X-ray Telescope.
Small-scale differential non-linearity was also determined to have an
RMS deviation from the mean of less than
0.1''.