*Doug.Henke@nrc-cnrc.gc.ca Optical design study for an 850 GHz commissioning camera module for CCAT-prime Doug Henke*a, Doug Johnstonea,b, Lewis B.G. Kneea, Scott Chapmanc, Colin Rossc, Michel Fichd, Thomas Nikolae, Steve K. Choif, Michael D. Niemackf,g, Stephen C. Parshleyf, Gordon J. Staceyf, Eve Vavagiakisf aNRC Herzberg Astronomy and Astrophysics Research Centre, Victoria, BC V9E 2E7, Canada; bDept. of Physics and Astronomy, Univ. of Victoria, Victoria, BC V8W 2Y2, Canada; cDept. of Physics and Atmospheric Science, Dalhousie Univ., Halifax, NS B3H 4R2, Canada; dDept. of Physics and Astronomy, Univ. of Waterloo, Waterloo, ON N2L 3G1, Canada; eCornell Center for Astrophysics and Planetary Science, Cornell Univ., Ithaca, NY 14853, USA; fDept. of Astronomy, Cornell Univ., Ithaca, NY 14853, USA; gDept. of Physics, Cornell Univ., Ithaca, NY 14853, USA ABSTRACT The CCAT-prime telescope, also known as the Fred Young Submillimeter Telescope (FYST), has an unblocked 6-m aperture designed for an extraordinarily wide field-of-view to be used in cosmological and galactic studies. Located at 5600 m near ALMA, the site has extremely dry conditions which make it particularly suited for observations at shorter sub-mm wavelengths. These attributes make CCAT-prime a potential platform for the next generation “Stage IV” cosmic microwave background experiment to conduct cosmology surveys of the extragalactic sky. CCAT-prime is also ideal for polarization studies within the galaxy and time-domain observations of nearby protostars. Prime-Cam is the wide-field, first-light instrument for CCAT-prime which, when complete, will contain seven instrument modules, including cameras and spectrometers, spanning mm through sub-mm wavelengths. Not all receiver modules are currently funded—including the 350 mm (~850 GHz) camera module that motivates the extraordinary high site of CCAT-p. Recognizing that an 850 GHz commissioning camera may be needed within the next 1–2 years, an optical design study was initiated where we purposely chose to reduce the scope, cost, and complexity while still preserving diffraction-limited optics, allowing for early science until the more powerful wide field science-grade camera module replaced it. In order to minimize the cost and scope of an 850 GHz commissioning camera, the optics plan for reuse of existing detectors (ACT MBAC TES detectors or BLAST-TNG MKIDs) and interface with the existing instrument module cartridge planned for Prime-Cam. Further simplifications include restricting the field-of-view and utilizing on-axis HDPE lenses without an anti-reflection layer. Discussion of optimal detector array F-lambda scaling, analysis of power loading, and feed horn coupling efficiency is included.