Apparatus for obtaining an image of a specimen (6) by optical projection tomography comprises a confocal microscope which produces a light beam which scans the specimen (6) whilst the latter is supported in a rotary stage (7). Light passing through the specimen is passed through a convex lens (8) which directs, onto a central light detector of an array of detectors (9), light which exits or by-passes the specimen parallel to the beam incident on the specimen.