Main Menu
|
I cast some concrete tools
reinforced with glass fiber using the blank as a mould. I then
covered the surface with 1" square tiles. As the curve had
already been generated I started with sandblasting grit. This turns
to sludge pretty quick but is cheap and I think leaves smaller pits
than 80 carbo. The marks left by the diamond wheel were quickly
removed then it was on to medium then fine powers. The only hiccup
occurred when I knocked the side of the mirror against a piece of
wood when moving it. The crack while small and not near the surface
was still unwelcome. |
|
|
I had started the mirror in June
and by August I had a mirror I could start to figure. The
parabolisation was difficult (f now 3.8) and lots of correction is
needed. I ended up using 3 different sized laps and a small tool.
When I finally got the reading to 1/4 wavelength I had picked up
some astigmatism. The mirror was 1/4 over in one axis and 1/4 under
in the other. For such a large mirror this isn't bad (I think).
However I tried to fix it but made things worse. Ended up going back
to medium grit and starting again. October I was again figuring.
Again got the figure close when astigmatism set in. Gave up at this
stage and sent the mirror to be figured professionally by Norman
Oldham (Oldham
optical). The problem was apparently that the back of the
mirror wasn't flat. Norman ground the back flat then completed the
figuring. Norman also made a 100mm flat. |
|
|
The Poor Meadow Dyke Galleries are now open. THE
GALLERIES |
See the full range of Atik cooled CCD cameras for
astronomy on the Atik Website
|
|
|