TABLE 4
              Characteristics of the WAC design

Optical        All reflective, two-mirror 20 deg off-axis
concept        design, unobstructed, unvignetted;
               axis of off-axis: y
FOV            11.35 deg (y)  12.11 deg (x)
Encircled      > 80 % inside a pixel of 13.5 um sq.
Energy
FL at centre   tangential: 131 mm, sagittal: 140 mm
of FOV
Average image  7.4 mrad mm-1 equiv. 101 urad px-1
scale at the
centre of FOV
Distortion of  Barrel type
the field
FL in x        128.0 mm to 133.4 mm
FL in y        139.2 mm to 140.0 mm
Residual       < 2.5 % along the tangential direction
geometric      < 1 % along the sagittal direction
distortion
Refocusing     No refocusing necessary for distance range
               500 m to infinity
Nominal F-     F/5.6
ratio
Wavelength     240 nm to 720 nm
range
Overall        52 % at 245 nm to 88 % at 500 nm
reflectivity