: I have a rather interesting problem. My father started grinding a 6" f/8 mirror blank some 40 yrs ago. He gave me the blank and tool around 9 years ago. I finish ground the blank, tested for radius of curvature using focault test, finish polished the blank then parabolized the blank. Before I was able to send the blank out for coating my father nad I had a disagreement and he asked for all of his things back. In January of this year he brought me the blank back. I began work on the scope again and was preparing to send the blank out for coating. On a whim since it had been so long since testing I placed the mirror blank in its cell and the tube and viewed the moon with it. I was not able to bring the moon into focus at all. Which leads me to believe I made errors in my original tests. Where would be the best place for me to start in determing what my problem is? Thanks for any input. The first thing i would ask you assuming that when you first made the mirror and applied the proper test procedures is were you able to focus in and out on the moon a mirror has to be pretty bad not to produce an image of the moon if you were not able to focus in and out you may want to check the focal length of the mirror and make sure the distance between the primary, secondary and focuser is correct regards tom soden