Is my TDE gone?

Michael Pendley (mycall@sandia.gov)
Thu, 13 Jul 1995 11:06:54 -0600

I had been trying to get rid of the TDE on my 12.5 inch mirror for weeks with my 10 inch plate glass tool. The advice to make a full size tool given to me by this list was exactly right. 2 hours of center over center, short stroke, 5 min. of polishing followed by 5 min. of pressing looks like it removed the TDE.

The Foucault images look pretty good. Quick and dirty numbers show a 1/3 wave figure (so I still have a ways to go) but I am not good enough at reading the shadows to know if I still have a TDE.

The Ronchi test shows a pattern like the one predicted by Mel Bartels program with a slight discontinuity at the very edge. Is this an indication of a slight TDE or is this discontinuity caused by some defraction effect at the mirror edge?

I also have two other misc. questions that someone may be able to help with

1) To get a high precision measurement of the focal length of the mirror do I divide the radius of curvature of the center zone by 2 or the .707 zone by 2 or what?

2) Just after a figuring session, while the mirror is reaching equilibrium, will the drift in zone readings tend to increase in radius of curvature or decrease?

Thanks