proto-Lightspeed: a high-speed, ultra-low read noise imager on the Magellan Clay Telescope

proto-Lightspeed is a new instrument that has been commissioned on the Nasmyth East port of the Magellan Clay Telescope at Las Campanas Observatory to deliver high-speed optical imaging with deep sub-electron read noise. Making use of commercial re-imaging lenses and the ORCA-Quest 2 camera from Hamamatsu, proto-Lightspeed images a field $1’$ in diameter at up to $200$ Hz or windowed fields at higher rates, up to 6600 Hz for a $1.6’’\times 1’$ field of view. proto-Lightspeed delivers seeing-limited image quality in the $g’$, $r’$, and $i’$ bands and adjustable magnification for pixel scales between $0.017’’-0.050’’$. proto-Lightspeed is well suited to studying compact binary systems, exoplanet transits, rapid flaring associated with accretion, periodic optical emission from pulsars, occultations of background stars by small trans-Neptunian Objects, and any other rapidly variable source. proto-Lightspeed will be a P.I. instrument beginning in 2026B, available for use by members of the Magellan Consortium. In this paper, we discuss the design and performance of the instrument, results from its two commissioning runs, and plans for a facility instrument, Lightspeed, to support simultaneous multicolor imaging across a $7’\times4’$ field.

💡 Research Summary

This paper presents the design, performance, and commissioning results of “proto-Lightspeed,” a new high-speed optical imager installed on the Nasmyth East port of the 6.5-meter Magellan Clay Telescope at Las Campanas Observatory. The instrument’s primary innovation lies in its use of a Deep Sub-Electron Read Noise (DSERN) CMOS image sensor, specifically the Hamamatsu ORCA-Quest 2 camera, which enables ultra-low read noise (≈0.3 e-) at very high frame rates. This addresses limitations of traditional high-speed imagers based on CCDs or EMCCDs, which suffer from higher read noise and excess noise factors at high speeds.

Proto-Lightspeed images a 1-arcminute diameter field at up to 200 frames per second (Hz). By windowing to a smaller region (1.6" x 1’), it can achieve rates as high as 6600 Hz. The optical design utilizes commercial off-the-shelf (COTS) components for rapid development: a Canon EF 400mm lens acts as a collimator, and a Canon RF 100-300mm zoom lens serves as the re-imager. This configuration provides variable demagnification, allowing users to select pixel scales between 0.017 and 0.050 arcseconds per pixel. This flexibility supports both conventional wide-field imaging and high-resolution speckle interferometry modes. The instrument is equipped with a filter wheel containing Sloan Digital Sky Survey (SDSS) g’, r’, and i’ band filters, and a separate linear stage can insert narrow-band filters (e.g., H-α) into the collimated beam.

The paper details extensive laboratory characterization of the ORCA-Quest 2 camera, confirming its low read noise, dark current, and high quantum efficiency. It also discusses calibration procedures for flat-fielding and nonlinearity correction, which are crucial for precision photometry. The software pipeline for instrument control, data acquisition, and real-time display is also described.

Two commissioning runs at the telescope demonstrated that proto-Lightspeed delivers seeing-limited image quality. Early on-sky observations validated its performance for studying rapidly variable astronomical phenomena. The instrument is well-suited for a broad range of science cases, including observations of compact binary systems, exoplanet transits, stellar flares, optical pulsars, and occultations by trans-Neptunian objects.

Finally, the paper outlines the future development of “Lightspeed,” a planned facility-class instrument that will expand upon proto-Lightspeed’s capabilities. Lightspeed is designed to provide simultaneous five-color (u’, g’, r’, i’, z’) imaging across a larger 7-arcminute by 4-arcminute field of view, with frame rates exceeding 8000 Hz in windowed mode. Proto-Lightspeed thus serves as both a powerful new tool for time-domain astronomy and a critical pathfinder for the next generation of high-speed, low-noise imagers based on CMOS sensor technology. It will be available as a principal investigator instrument for the Magellan Consortium starting in the 2026B observing semester.