Hmmm, dilemma of choosing which path to take Both are fairly new to me so it's going to be a challenge.
@Pinbout, that video makes it fairly clear the approach you suggested.
@dogbiscuit, yes the mirror is fully polished. Wouldn't working ToT be risky and potentially create a TUE? Also, would it flatten the center?
Thanks gentlemen for your kindhearted suggestions! I will update once I execute one of these two approaches.
Within the limits of what can be seen in Ronchi your edge looks perfect. I think Foucault shows the edge better. I'm pretty sure Foucault test would show a very well balanced diffraction ring around your mirror.
You do have under correction in the outer zones so you could view that as a turned up zone, but the edge is near, maybe is perfect. For me when speaking of turned up or down edge, that is really the last mm or two at the edge. Much wider than that it becomes a zone.
"Wouldn't working ToT be risky and potentially create a TUE?"
I'm pretty sure you made a typo and meant to say TDE.
Your edge is so good almost anything you do could make it worse.
The stroke shown works fine for me. The edge on the mirror in the video is also near perfect but my lap is always maintained in perfect condition, channels uniform and well pressed, and work done at controlled temperature.
The TOT large W shown rolls correction into the outer zone. There is a knack to sizing the W to get just the right gradient of correction across the outer zone, and I would do only 1 turn around the mirror with the stroke shown and see what and how much happens and adjust if another round is needed. Wouldn't take much for an 8" f:6. Might be 1 turn would do it. Doesn't seem there are many mirror makers using this method. Maybe it's not really as easy as I find it to be for correcting outer zones.
The video link was as much to show stroking method as the particular stoke itself.
Go with Pinbout's suggestion.
Try my method on some future mirror or if something bad happens and you start from a sphere again on this one. When I use this method it is 1 or 2 turns of MOT classic parabolizing stroke and an equal amount of TOT parabolizing stroke. Then adjust the ratio of MOT to TOT and maybe size of the Ws depending on test results.
Edited by dogbiscuit, 14 October 2021 - 04:12 AM.