harness are constructed and fitted to the glass blanks. After this has been completed, the mirror blanks are fine-ground and polished.
After the mirrors have been tested and found to have the desired surface curves, the warping harness is tested with the secondary mirror in the test set-up shown in Figure 4. After the warping harness has passed its test, the radii of curvature of the two mirrors are measured carefully, and a second design is made, based on the measured values of the radii of curvature of the two mirrors as they have actually turned out, Eq. (6). Usually, the new value of mirror-separation, S, will turn out to be not greatly different from the first calculated value, and the plans as first laid out can be altered fairly easily to conform to the new values.
The telescope tube and baffle system is constructed next, based on this second design. Finally, after the tube has been built, the actual separation distance, S, is measured, and the angle B, is calculated from measurements of the primary mirror relative to the line running from the center of the eyepiece tube to the center of the secondary mirror. With these final values for S and B, a third design is calculated (mainly the angle, A) using Eq. (5). Final collimation of the instrument is carried out according to this final design.
The purpose of the warping harness is to produce, by mechanical flexure, a displacement of the mirror surface which is everywhere equal and opposite (to within acceptable optical tolerances) to the wave-front aberration, astigmatism. The aberration, astigmatism, is given by the following equation: