All-optical electrophysiology (Optopatch), a technique ce-developed by Dr. Farhi while in Dr. Adam Cohen's Lab, combines a spectrally orthogonal channelrhodopsin and archaerhodopsin-based voltage indicator. Cotransfection of cells with both constructs enables bi-directional control and readout of neuronal activity at throughputs dramatically higher than those possible with conventional electrophysiological measurements. However, archaerhodopsin-based voltage imaging has stringent technical requirements due to the fast frame rates (>500 Hz) and low brightness of the indicator. We have thus built a custom “medium-field” pseudo-total internal reflection microscope, which tightly illuminates cells grown in culture with a thin light sheet propagating through the plane of the cells (Nguyen et al., 2019). This configuration dramatically reduces fluorescent background from the media and illumination optics. The imaging configuration can achieve 1000 Hz imaging over a 2.2x0.2 mm field of view with a numerical aperture of 1.0.