A compact grism spectrometer for small optical telescopes

We describe a low-cost compact grism spectrometer for use with small astronomical telescopes. The system can be used with existing charge-coupled device (CCD) cameras and filter wheels. The optical design consists of two prisms, a transmission grating, a collimating lens, and a focusing lens, all enclosed in a 3D-printed housing. The system can be placed inline, typically in an unused filter wheel slot. Unlike conventional spectrometers, it does not require the target to be precisely positioned on a narrow slit. The mean resolving power (⁠$R≈$ 300) is sufficient to resolve the spectral lines of many astronomical objects discussed in undergraduate astronomy labs, such as stellar absorption lines along the main-sequence, emission lines of early type hot stars and galactic novae, and redshifts of bright quasars and supernovae.