I have had a reply from Bill @ astronomyasylum.com with a link showing how Celestron corrector were made which is interesting. It shows that the individual figuring was all done on the secondary and shows the vacuum form mould method for the secondary which might explain slight variations in centering. It would be interesting to see the books about SCT by Bob Piekiel
http://theketelsens.blogspot.com/201...ing-night.html