An advanced development of the *phase contrast microscope
in which the light from the condenser is split into two beams by a prism. The object beam passes through the specimen and the objective; the reference beam passes through a second matched objective without going through the specimen. The two beams are recombined before going through the eye piece. Interference between the beams produces a series of light and dark fringes in the field of view. These are the result of differences in refractive index of the specimen and allow detail of the specimen to be seen. The instrument is more sensitive than the phase contrast microscope and spurious effects (such as halos) are eliminated. With white light different parts of the specimen appear coloured as a result of interference.