Subject: new secondary for the 3.5m

From: Patrick Waddell

Submitted: Mon, 28 Jul 1997 12:00:42 -0700

Message number: 159 (previous: 158, next: 160 up: Index)

This note is to clarify the status of the new secondary for the 3.5m
telescope.  My appologies if this information was not widely circulated
earlier.

On September 18, 1995, Hextek completed fabrication of a blank for the 3.5m
telescope replacement secondary.  In early October '95, a detailed
inspection revealed that, although the faceplate had some departure from
sphericity, which would ultimately lead to nonuniformity in faceplate
thickness when finished, the part was better than the original 33" blank
and was acceptable.

In mid-January '96, Hextek was given the go-ahead to do further work on the
blank to prepare it for final optics figuring, which included:

- The overall faceplate and backplate diameters were ground to 32.90" +/-
0.02".

- The center back plate was bored to 2.16" diameter, concentric with the
faceplate to +/- 0.1".

- The three support holes in the back plate (120deg apart on a radius of
8.66" from the center) were bored to 2.16" diameter.

- The remaining cell holes were enlarged for ventilation.

- The front surface was fine ground to a radius of curvature of 125.342"
+/- 0.01" over 12" spatial scales.  The surface figure is better than 1.5
fringes (650 nm) over 7" spatial scales.

These efforts were completed on July 11, 1996 and the secondary was shipped
to JHU.

-pw



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