Method for calibrating a phase mask, in particular a spatial light modulator, in a beam path of a light-sheet microscope for examining a sample, wherein the light-sheet microscope comprises at least one light source for emitting illumination light, at least one microscope objective for guiding the illumination light onto the sample, and optical means (40, 50, 64) for guiding detection light from the sample onto a camera (62, 66), wherein the phase mask to be calibrated is arranged in the beam path between the light source and the at least one microscope objective of the light-sheet microscope, wherein in the method the following method steps are performed: the phase mask is actuated successively with different patterns (Gi(x,y)) of grey levels, wherein a first grey level of a first partial quantity of segments remains constant, and wherein a second grey level of a second partial quantity of segments is varied from one pattern (Gi(x,y)) to the next pattern (Gj (x,y)), at least one part of the total intensity of the light in the beam path is measured downstream of the phase mask for the different patterns (Gi(x,y)) and a characteristic (I) of the measured intensity is obtained in dependence on the second grey level, a relationship (φ) between the second grey level and a phase shift (φ), which is imprinted by the phase mask, is obtained from the characteristic (I), and an actuation of the phase mask is calibrated on the basis of the obtained relationship (φ) between grey level and phase shift (φ), characterized in that the phase mask for the calibration measurements is exposed to light from the light source, in that light reflected at an object carrier for holding a sample or at a cover slip is used for the measurements for the calibration, wherein either the detection beam path is free of filters for blocking illumination light or filters for blocking illumination light in the detection beam path are removed from the beam path for the measurements for the calibration, and in that a structured illumination in the form of an intensity grid is provided by the phase mask. the phase mask is actuated successively with different patterns (Gi(x,y)) of grey levels, wherein a first grey level of a first partial quantity of segments remains constant, and wherein a second grey level of a second partial quantity of segments is varied from one pattern (Gi(x,y)) to the next pattern (Gj (x,y)), at least one part of the total intensity of the light in the beam path is measured downstream of the phase mask for the different patterns (Gi(x,y)) and a characteristic (I) of the measured intensity is obtained in dependence on the second grey level, a relationship (φ) between the second grey level and a phase shift (φ), which is imprinted by the phase mask, is obtained from the characteristic (I), and an actuation of the phase mask is calibrated on the basis of the obtained relationship (φ) between grey level and phase shift (φ), characterized in that the phase mask for the calibration measurements is exposed to light from the light source, in that light reflected at an object carrier for holding a sample or at a cover slip is used for the measurements for the calibration, wherein either the detection beam path is free of filters for blocking illumination light or filters for blocking illumination light in the detection beam path are removed from the beam path for the measurements for the calibration, and in that a structured illumination in the form of an intensity grid is provided by the phase mask.