A serious problem has become apparent. The image formed has considerable astigmatism. This astigmatism is not of the ordinary type where a line becomes an ellipse which rotates becoming a line again as one changes the focal position. Instead, the image, at best focus, has three or four spikes which extend in rather odd angles to each other, extending some 4 mils outward from the center of the main blob. These spikes rotate as the corrector is rotated and so must be a feature of the corrector plate.
Lets start with the cause.
I did not rotate the corrector with respect to the vacuum pan during grinding and polishing. So, if the vacuum pan lip is not flat then I could have caused the astigmatism by not rotating the blank. Since I ground and polished both sides of the plate, I could have put astigmatism on both sides, at odd angles to each other. This would explain the multiple spikes that I see. Since I need to polish the corrector anyway to remove the remaining spherical aberration, I may be able to remove the astigmatism at the same time by polishing for a while, turning the plate with respect to the vacuum pan and polishing some more.