With the BH Modular Series, launched in 1974, the microscopes could be transformed to meet various specifications, including polarization, phase contrast, differential interference, and simple transmission fluorescence microscopy. The previous E and F Series of microscope bodies and the POS and POM models were specialized devices with more restricted uses or specifications. The BH Series, however, could be used for a wide variety of observations simply by switching the microscope head or lens modules. The BH Series was also the first Olympus product to feature a coaxial handle attachable to the left of the plane stage, which allowed the stage to be easily moved on a vertical or horizontal axis.
Olympus launched the BHA and BHB models for research and test purposes, whereas the BHC model was meant for test and practical study. The BH Series was subsequently developed further into the BH2 and the BX.