|
|
||
Upper End |
WIRCam mounts on the "old" CFHT prime focus upper end (PFUE), previously used with the CFH12K and UH8K cameras (and in much earlier days with photographic plates). The old optical corrector has been removed (now precluding use of CFH12K as a backup for MegaPrime), and CFHT staff has thoroughly renovated the mechanical and electrical environment of the upper end. In addition to its basic structure, the PFUE provides a temperature controlled environment for WIRCam and its readout electronics, and brings the instrument into focus. | ||
|
|
||
Image
Stabilizing Unit |
The Image Stabilizing Unit (ISU) has
been designed and built at Observatoire de Paris.
It is used to produce small corrections of the image position on the
focal plane of WIRCam: a glass plate in the optical beam in front of
the camera can be tilted, to produce a displacement of the image
proportional to the small angle of the tilt. The guiding signal is
obtained from the scientific detectors themselves, on which a small
guiding window can be read out at a high rate. The guiding window can
be positioned anywhere within the detector.
|
||
|
|
||
Detectors | The detectors at the heart of WIRCam
are HAWAII-2RG
detectors, produced by Rockwell
Scientific.
|
||
|
|
||
Optics |
The optics
which focuses the infrared light on the WIRCam detectors was designed
and
assembled by the Laboratoire d’Astrophysique Expérimentale of Université de Montréal and the Institut National d'Optique in Québec
city. It features one of largest cryogenic refractive optics in the
world consisting
in 8 lenses made of fragile crystal materials and a cryostat window. To
minimize its own emission the optics is housed inside the WIRCam
cryostat. It
is therefore subject to significant thermal contraction, and its large
physical
size made this an interesting mounting and alignment challenge. All
lenses are
aligned with one another with a precision better than 25 µm or
half the width
of a hair.
|
||
|
|
||
Mechanics | The mechanical structure of WIRCam and
its cryogenic systems were designed by the Laboratoire
d'Astrophysique de Grenoble. The structure was optimised to have
extremely low flexures, and the large filter wheels to have reliable
fast movements in the cold (15s maximum time for filter changes). |
||
|
|
||