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CCD NEWS (1Dec93)
(from CTIO, NOAO Newsletter No. 36, 1 December 1993)

                         ArCon and the Tek 2048

The Tek 2048 CCD is now operating with an ArCon controller, reading out
through two amplifiers. After some teething troubles (we thank the
first few observers for their forbearance) the CCD is now working well.
At a pixel time of 7 us, the gain is 3.2 e-/adu, the read noise 4.0 e-
rms, and the read time is 75 seconds.  This setting matches the dynamic
range of the CCD (220000 e- full well) and is invariably the
setting-of-choice for direct imaging. For use at low S/N, for example
with the Echelle long camera, a 20 us pixel time yields a gain of 1.1
e-/adu, read noise of 2.8 e- rms, and a read out time of 127 seconds.
The most notable improvement over the old VEB-controller
implementation, apart from the shorter read times, is the lack of fixed
pattern noise and much lower read noise at short pixel times.

                          4-m Prime Focus Imaging

The Tektronix 2048 was used with the Large Format PF CCD and, for the
first time, with the new ADC corrector, for most of the 4-m prime focus
runs 7-20 September.  The CCD was controlled by ArCon, and the
instrument was operated with the new STD-bus controller.  Unlike the
hybrid arrangement reported in Newsletter No. 35, p. 15, all control of
instrument and CCD are integrated under the one user interface, which
is easy to use and operationally very similar to the KPNO "ICE"
interface. The optical performance with the new corrector is of great
interest, since it is designed to give 0.25 arcsec images over most of
a one degree diameter field. The ADC corrector is optically slower than
our older correctors (f/2.89, 18.0 arcsec/pixel) so the Tek 2048 has
pixel size 0.44 arcsec and field size 15 arcmin square. There is slight
curvature of field; this may well all be due to the CCD itself since it
is known not to be flat. If the CCD is focused so that best focus is
approximately midway from center to corner, then FWHM at the center and
corners will be about 0.06 arcsec larger than for the focus star. The
actual FWHMs observed were somewhat of a disappointment, with best
images around 1.1-1.2 arcsec FWHM.  However, we anticipate that the
seeing and optics improvement program presently underway should, in the
near future, allow the full capabilities of the new corrector to be
realized.

                          Schmidt (CCD) Focus Mount

The new focus mount for the CCD on the Schmidt telescope has been
mechanically completed, and placed into service. This work was funded
by the University of Michigan in a program to upgrade the CCD
capabilities of this telescope. Although the focus is still adjusted
manually, it is very much easier to do than before and projects using
several filters are now viable.  The motor controller for the focus
mount should be finished in a few months time, whereupon the focus will
be able to be controlled from the ArCon user interface.

Alistair Walker

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