When you did your 6" I had suggested a couple of relatively long strokes and then a large W parabolizing stroke.
post 84 here in thread for the 6"
The reason I chose those strokes to parabolize was that the basic parabolizing stroke in texereau's book (and most other sources) usually corrects the central area from from center out to about the 60% zone but adds very little correction from there to the edge. The books show two other parabolizing strokes, one to add more correction to the outer zone with more strokes in the center of the W, and another that has more strokes in the sides of the W for adding more correction to the mirror's center.
The three strokes I suggested accomplished something similar to doing the parabolizing stroke to add more in the outer zones. I think it might be simpler to do the two relatively long narrow W strokes that both have same spacing of strokes to get some correction in the outer zones plus the standard parabolizing W to correct the center areas.
If you watch the figuring threads, you will see that most people will have no trouble parabolizing from center to about the 60 or 70 % zone, then have difficulty getting correction into the outer zones. They work a while trying to get correction in the outer zones and end up overcorrecting the central zones.
So a little bit of the long narrow Ws can help you keep the correction in the outer zones near the same as the central zones. Try to keep correction about the same from center to edge.
Don't do too much of either the long narrow strokes or the standard parabolizing stroke.
You can do a little of the long narrow strokes to get some correction started in the outer zones.
Then the large parabolizing stroke can be used until the central correction starts getting to be more than the outer zones.
Then do a little more of the narrow strokes to even
And remember that last almost sideways stroke at the sides of the W is that way for a reason.
Edited by dogbiscuit, 15 September 2020 - 12:15 PM.