light arriving from the telescope first goes
through an atmospheric dispersion correc-
tor (ADC) that compensates for atmospheric
chromatic aberrations. The light then enters
the NIR cryogenic chamber, where it reaches
the focal plane unit. After the focal plane,
the light is divided by the first dichroic into
NIR and Visible (VIS) light. The VIS light then
leaves the cryogenic chamber through a
second window to the VIS bench which is
at approximately the same temperature as
the telescope. From there, the light of both
beams follow similar paths, where the light
is collimated and subsequently split by addi-
tional dichroics. The collimated beam of each
arm passes through either a filter or grism,
depending on the observing mode, and is
refocused by a camera onto the detector.
As the OCTOCAM block layout diagram
shows (Figure 3), the design is highly sym-
metrical, with the VIS and NIR arms each
sharing their own common optics among
themselves. Symmetry helps to constrain the
effect of the mechanical flexures occurring
during motion at the Cassegrain mount. All
wavelengths share a common optical path
to the focal plane, where the focal plane car-
riage positions the slit. The single slit design
will ensure that all the spectrographs are fed
by light from the same sky aperture and pro-
vides better data calibration. The simultane-
ity of OCTOCAM’s eight arms make it very fast
to calibrate and extremely easy to operate.
The Gemini OCTOCAM project team consists
of Stephen Goodsell (Program Manager),
Morten Andersen (Project Scientist), Jeff
Radwick (Project Systems Engineer), Cathy
Blough (Project Specialist), and Rubén Díaz
(Instrument Program Scientist). Both the ex-
ternal team and Gemini staff will work col-
laboratively to complete the Conceptual
Design later this year. We look forward to
sharing this instrument’s adventures in the
years to come.
Stay tuned, and see this webpage for the lat-
est information.
Stephen Goodsell is the Gemini Instrument Pro-
gram Manager and located at Durham Univer-
sity. He can be reached at: [email protected]
FIgure 3.
Block layout diagram of
OCTOCAM, showing its
highly symmetrical design.
18
GeminiFocus
April 2017