From edo@as.arizona.edu Fri Jan  4 15:04:44 2002
Date: Fri, 7 Dec 2001 11:05:25 -0700 (MST)
From: E. Olszewski <edo@as.arizona.edu>
To: ggwilli@as.arizona.edu
Subject: what i just sent to cambridge and to chile

>From edo Fri Dec  7 11:04:32 2001
Date: Fri, 7 Dec 2001 11:04:29 -0700 (MST)
From: "E. Olszewski" <edo>
To: awalker@noao.edu
Cc: bmcleod@cfa.harvard.edu, edo
Subject: my prime focus camera for Steward 2.3m

Alistair,

.
.
.

You can see the optical layout at 
http://compton.as.arizona.edu/90prime/pictures/optics/optics7.gif

So the new chip and ding are on L2. the old ding, again from a tool
being dropped, is on L3, and 
"It is a hole in the glass that happened during fabrication.  It was probably
the pin slipping out of the tooling and impacting the surface.  The hole is
about 1.75" from the edge, 3/32" across and 1/32" deep.  It appears to have
been drilled out after the damage occured."

the chip is 
"I have evaluated the chip in L2 and recommend that we proceed with the part,
then paint the area black before installing the lens.
The chip is big and ugly, but the area it extends into the clear aperture is
only about 8 mm across.  The beam is 200 mm across here, so worst case, it
affects 0.16%.
In fact, we can do much better then this.  If we clock the chip so that it
is oriented along the sides (not the corners) of the filters and the CCD,
then it will never be seen by the focal plane.  We do need to make sure that
we do NOT put it on the side of the guider."

the ding in L2 is
"This morning it was reported that  we suffered additional damage on the =
L2 spherical surface.  This time it was Dean and he pinged the surface =
with the drive pin while adjusting it for a polishing run.  It is a =
small (~1mm diam) on the surface near the center.  It has also a typical =
conical fracture that extends into the depth of the glass probably more =
than a mm but is difficult to quantify since the fracture edge is not =
easily seen. =20
Jim was over here this morning and he and I examined it closely.  Jim's =
opinion is that the defect itself is small enough to ignore.  Typically, =
we would grind out the fracture as we did for L3 but I am reluctant to =
carve a hole in the surface  since it will increase the size of the =
unusable area.  We were concerned over the possibility that the fracture =
may propagate so we looked at it under crossed polarizers and can detect =
virtually no stress birefringence.  So it is unlikely that the fracture =
will propagate.  However, if the coating temperature is very high it may =
make the fracture move.=20
Jim suggested I speak with the coating vendor to determine what the =
optic will be subjected to in coating so I would like the contact =
information for the coater from you along with some way to identify the =
coating to the vendor so he knows which one I'm talking about.
"

.
.
.

thanks

edo