Optics
I refigured the primary, but first I had to strip off a 25 year old Beral
coating. It was still reflective, but full of holes. If only they
made them like the used to - they don't last this long any more, it seems.
Here's a photo of the primary being stripped, and a refiguring lap being
pressed. Refiguring was done with a lap that was just small enough to
be pressed between the edge of the mirror and the edge of the central hole.
A more thorough discussion of Cassegrain secondary figuring can be found
in my page on the optics
of the 16.26" CUAS Cassegrain. Here's a photo of the pitch laps
for both Cassegrains, for both the test plate and mirror. The concave
test plate was figured first, and was Foucault tested with two different Couder
masks. Its overall figure was quite good, with a slight dip near the
90% zone. The secondary was then figured to match the test plate using
contact interference testing (again, see the other Cass. page, or my "Tale of Four Flats").
The second photo is the interference test of the secondary in the middle
of figuring.
Finally, here's another test image during figuring, and the final test.
The dip in the 90% region is on the test plate, as is the edge roll.
