light arriving from the telescope first goes through an atmospheric dispersion corrector ( 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 additional 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 symmetrical , 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 carriage positions the slit . The single slit design will ensure that all the spectrographs are fed by light from the same sky aperture and provides better data calibration . The simultaneity 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 external team and Gemini staff will work collaboratively 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 latest information .
Stephen Goodsell is the Gemini Instrument Program Manager and located at Durham University . He can be reached at : sgoodsell @ gemini . edu
FIgure 3 . Block layout diagram of OCTOCAM , showing its highly symmetrical design .
36 GeminiFocus January 2018 / 2017 Year in Review