To observe the interference figure, true petrographic microscopes usually include an accessory called a Bertrand lens, which focuses and enlarges the figure. It is also possible to remove an eyepiece lens to make a direct observation of the objective lens surface.
When utilizing a petrographic microscope, observing the interference figure typically requires the use of a Bertrand lens for enhanced visualization. However, removing the eyepiece lens also allows direct observation of the objective lens's surface.