BLUE contrast filter for biological microscopes with a diameter of 32 mm mounted in the filter holder under the microscope table. The task of colored filters (yellow, green, blue) is to improve the spectrum (improvement of the color temperature) of the light illuminating the preparation. This is especially important for photomicrography. In the case of viewing colored preparations, filters improve their clarity and contrast. The filters are also used in the so-called Optical play of the preparation, and in the case of the use of techniques related to the dark field may be a component for obtaining the so-called Rheinberg lighting - obtaining a colorful background.