A sensor assembly includes: a sensor including pixels that are aligned in a predetermined direction, the pixels being for detecting an electromagnetic wave; and a lens that forms, in a detector plane on the sensor, an image according to the electromagnetic wave, wherein the lens has an f-number in a first direction and an f-number in a second direction, the f-number in the first direction being different from the f-number in the second direction, the first direction being orthogonal to the predetermined direction in a plane parallel to the detector plane, and the second direction being the predetermined direction. For example, the f-number of the lens in the first direction is smaller than the f-number of the lens in the second direction.