OSMOS (Ohio State Multi-Object Spectrograph) is a wide field imager and multi-object spectrograph that was commissioned at the 2.4m Hiltner telescope at the MDM Observatory in April 2010. OSMOS employs an all-refractive, zero-deviation design that projects a plate scale of 0.3-arcsec/pixel and a 20-arcmin diameter FOV onto the MDM4K or R4K detector systems. There is a 6-position slit wheel, a 6-position disperser wheel, and two 6-position filter wheels. The slit wheel may contain either long slits or customized masks that are laser cut into spherical, NiColoy masks that match the curvature of the 2.4m focal surface. Up to 50 to 100 slitlets should be feasible per mask. The current complement of dispersing elements includes a very low resolution triple prism and a high-efficiency, low-resolution VPH grism (R=1600, peak at 450nm).

The design of OSMOS was very successful and cloned for the KOSMOS and COSMOS spectrographs that OSU built for the US National Observatories (now NOIRLab) for the 4m telescopes at Kitt Peak (KOSMOS) and CTIO (COSMOS).