Subject: DIS blue side returned to service & upgrade completed

From: Ed Turner

Submitted: Fri, 24 May 2002 15:29:43 -0400 (EDT)

Message number: 580 (previous: 579, next: 581 up: Index)

I am happy to announce that the blue side of DIS has been returned to
service and is expected to be ready for on-sky science use tonight.  We
were fortunate to be able to get a replacement chip very quickly and thus
the down time was at the very minimum end of the range anticipated when
the old chip was damaged (see apo35-general message #570 issued on April
26).  Additional good news is that the new chip is of somewhat better
quality than the one it replaced, having better cosmetic quality and
slightly better QE than the old chip.  Its read noise is the same, about
4-4.5 electrons.

Furthermore, the improperly AR coated field flattner lens in the DIS blue
camera has been replaced with a new and correctly coated one.  This will
restore throughput between about 3800 and 4600 Ang.  See apo35-general
message #559 for a description of the problem with the old lens.

Thus, although there remain some relatively minor electronics enhancements
and debugging to be done to achieve optimal performance, the DIS upgrade
and repair is now essentially complete.  Both the APO staff and the UW
engineering group have worked hard to achieve this very considerable
success and deserve the thanks of the user community.

I would very much like to see comparison spectra taken of the same
(non-variable!) object with the same exposure time and under similar
conditions with the old and upgraded DIS.  If anyone obtains such, please
provide me with copies of the spectra if possible.

Ed Turner


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