This device, built as an accessory in the early 1970s, was attached to Nikon microscopes to allow observation and discrimination of minute differences in thickness and refraction of non-stained transparent specimens, making it possible to estimate phase and refractive index differences.
This feature was of particular importance in observing living specimens, which themselves have little or no inherent contrast. Details of the organisms could be detected by color differences and they could be also observed under conditions of continuously changing contrast.
The interference-phase accessory was mounted between the eyepiece tube and the microscope body. Incorporated into the unit was a 180° rotatable polarizer, quarter wave plate, phase rings and a 90° rotatable analyzer. A turret condenser, equipped with housings for beam-splitting prisms, replaced the regular microscope condenser. A centering telescopic eyepiece, for alignment of the optical accessories, was provided with the attachment and would replace the standard monocular eyepiece or one of the two eyepieces in a binocular model. Green and heat-absorbing filters were also provided for infrared-free monochromatic light.