Abstract: This invention relates to a method and apparatus for exposing a photosensitive film on a holographic plate to fabricate a reflective holographic optical element. The apparatus incorporates compensating means which are adapted to compensate for the effects of refractive index shift of the film due to refractive index variations during the exposure process. In one form of the apparatus, a hologram-mirror arrangement is placed on a table on an accurately controlled stepper motor rotating stage so that the table is progressively tilted. In an alternative arrangement the angle of the exposing radiation beam is changed and directed on to the stationary hologram-mirror arrangement. Where a tuneable holographic filter is required where the exposure angle varies over the hologram aperture angular shift is achieved by simple lateral and linear shift of the hologram. The compensating means can also comprise an arrangement for progressively changing the wavelength of the exposing radiation beam.