A pixel array for imaging comprises an array of pixels of a first pixel type and a second pixel type. Each pixel of the first pixel type comprises a first photo-sensitive element having a first area. Each pixel of the second pixel type comprises a second photo-sensitive element and a third photo-sensitive element. The second photo-sensitive element has a second area, which is smaller than the first area. Only the second photo-sensitive element in the pixel of the second pixel type is connected to a readout circuit. The third photo-sensitive element is connected to a charge drain via a permanent connection or a switchable connection. Outputs of the second photo-sensitive elements can be used to perform phase detect autofocussing.