1. A method of imaging biological samples in wells of a well plate, the method comprising: defining a path across the well plate that includes each part of each well containing a sample to be imaged; moving the well plate with respect to an optical beam source operable to generate a beam of light to illuminate the sample in a well and an imaging camera operable to record an image of the sample of a well when illuminated so as to bring each part of each well in the path in turn into a position where the sample can be illuminated and imaged, the movement being continuous from a start to an end of the path; operating the optical beam source and the imaging camera to illuminate and image the sample in a well wherein only one part of each well is illuminated and imaged in each operation; and further operating the optical beam source and the imaging camera to illuminate and to image further part or parts of the well when they are in the position where they can be illuminated and imaged; wherein the well plate is arranged in a vacuum holder comprising a vacuum bed with a planar surface so that a lower surface of the well plate is flattened by vacuum pressure against the planar surface of the vacuum bed, thereby to ensure that the wells of the well plate are co-planar.