Left: The optical beam enters at the lower left through a CsI window (blue). The beam then encounters the field stop, an aperture wheel (green) located at the telescope focal plane. The light then reflects off the collimator mirror (blue, top-center) which images the secondary mirror of the SOFIA telescope onto a Lyot stop located between two filter wheels. The aperture wheel and collimator are attached to the liquid nitrogen (77K) work surface (yellow). The collimated beam then enters the liquid helium (4 K) section of FORCAST (pink surface). A dichroic slide directs the optical beam to the short wavelength channel (SWC) and/or the long wavelength channel (LWC), as indicated by the blue (SWC) and red (LWC) optical components. The dichroic slide contains a dichroic (wavelength splitter), a mirror, and an open position to allow channel selection. For each channel the collimated beam passes through a pair of filter wheels (white) before encountering a camera mirror which focuses light onto a focal plane.
Right: View of liquid helium (red) and liquic nitrogen (yellow) vessels, lower half of the outer vacuum shell (blue) and telescope mounting plate (black).