Abstract: Apparatus for and a method of optical inspection in a total internal reflection holographic imaging system. Multi wavelength laser beams are directed onto a prism supporting a first substrate containing pre-recorded hologram which is to be imaged onto a recording medium of a second substrate, the multi wavelength beams being normal to both substrates. The distance between the two substrates is measured by interferometric techniques. Actuators are provided for adjusting the distance between the two substrates, these actuators being energized to cause minute adjustments of the spacing during a scanning operation whereby the imaging of the pre-recorded hologram is ensured at the correct focus throughout the scanning operation.