A tomography accessory device for supporting a sample relative to the imaging assembly of a microscope has an electric positioning motor supported on the existing sample supporting stage of the microscope. An output shaft of the positioning motor is supported for rotation about an output axis parallel to a plane of the stage and a controller acts to control the motor so as to rotate the output shaft between a plurality of different angular positions about the output axis. An adjustable assembly supports a sample holder relative to the outer shaft such that i) the sample holder is translatable relative to the output shaft along at least one translation axis oriented generally perpendicularly to the output axis, and ii) the sample holder is pivotable relative to the output shaft about at least two pivot axes which are transverse to one another and which are generally perpendicular to the output axis.