ATM 4" ronchi, day 4

[Ron Forrester <rjf@skyhackers.org>]

Sure helps to have the correct number of lines entered for your
grating :)

Again, this is a 4.25" mirror with ROC of 50.25".

So tonight I did some 1/3 center over center strokes to try and rid
myself of the slight TDE. It seems to have worked, so I tried a quick
5 minutes of parabolization (1/2 long, wide W stroke), and I think I
got pretty close, anyone care to critique:

   http://www.skyhackers.org/ronchi/4inch-day4-1.jpg  (.3" inside ROC)
   http://www.skyhackers.org/ronchi/4inch-day4-2.jpg  (.7" inside ROC)
   http://www.skyhackers.org/ronchi/4inch-day4-3.jpg  (1" inside ROC)

My tester doesn't have enough travel, so the last two are estimated
distances (will fix my tester this weekend).

It's too bad I can't get the camera to take pictures outside of ROC,
as they really seem to confirm I got rid of the TDE and that I am near
if not on the parabola.

Something very interesting -- after the 1/3 COC strokes (mirror on
top) when I put it on the tester I could practically see the pitch
squares on the mirror (in the ronchigram) -- it took a 10 minute
session with standard W stroke to remove these 'artifacts', which by
the way, scared the sh*t out of me ;-)

I'd appreciate any feedback... I have another 4.25 sitting there
through fine grinding waiting for it's turn on the lap (which reminds
me, my pitch is hard, which I like, and I think I can just plop this
second mirror on the current lap after a little trimming, give it a
good warm press, and hit it, no?)

Thanks.
rjf&