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The WFC optics consist of a nested set of 3 Wolter-Schwarzschild Type I mirrors, fabricated from aluminium and coated with gold for maximum reflectance. The mirrors provide a geometrical collecting area of tex2html_wrap_inline17837 with a common focal length of tex2html_wrap_inline17839 . The grazing incidence angles chosen (typically tex2html_wrap_inline17841 ) allow the collecting area to be optimised whilst retaining a wide ( tex2html_wrap_inline17843 radius) circular field of view and a high-energy reflectivity cut-off at tex2html_wrap_inline17845 ( tex2html_wrap_inline17847 ).       The on-axis resolution is 2.3' HEW, degrading to tex2html_wrap_inline17851 HEW at tex2html_wrap_inline17853 off-axis due to inherent optical aberrations. The average resolution for the all-sky survey is tex2html_wrap_inline17855 HEW.     The mirror parameters are summarised in Tab. 6.1.    



Mirror type Wolter-Schwarzschild Type I
Mirror material Ni plated Aluminium
Reflective coating Au
Number of shells 3
Field of view tex2html_wrap_inline17857 diameter
Geometric area tex2html_wrap_inline17859
Aperture diameter tex2html_wrap_inline17861
Focal length tex2html_wrap_inline17863
Focal plane scale factor tex2html_wrap_inline17865
High energy cutoff (10% of peak) tex2html_wrap_inline17867
Half energy width (on-axis) 1.7' at tex2html_wrap_inline17871
Table 6.1: WFC mirror parameters

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