Some implementations of the disclosure relate to an imaging system, including: a sample holder to support a sample container having multiple sample locations; an optical stage having; an assembly comprising one or more actuators physically coupled to the sample holder to tilt the sample holder relative to the optical stage during imaging of the multiple sample locations to focus the optical stage onto a current sample location; a first light source to project a first pair of spots on the sample container; and a controller to control, based on a sample tilt determined from a first separation measurement of the first pair of spots from one or more images taken by an image sensor at one or more of the sample locations, the one or more actuators to tilt the sample holder along a first direction of the imaging or a second direction substantially perpendicular to the first direction.