Image-shearing apparatus comprises a television camera tube for receiving an optical image from a microscope objective. Electrical circuitry receives the output signal from the camera tube and provides a display image in which a horizontal band is uniformly shifted relative to the remainder of the frame. The amount of lateral shift is adjustable, preferably in a calibrated manner. Then, by registering an edge portion of the image in the shifted band with an adjacent edge portion outside the band, the apparatus may be used with particular advantage in sizing.