Infinity optical system with coaxial epi-illumination and polarizing device, suitable for a large platform and lifting column tall specimen, metallurgical testing can be used for large workpieces, large area silicon electronics industry, PCB and LCD etc. Configuration and dark-field and dark-field lens and lighting system to improve the resolution of the microscope, and things like the contrast and reduce glare interference, sample some of the inclusions are not visible, transparent particles, grains and grain boundaries inherent color can clear to show and compare, ratings and so on. ● trinocular five holes: 50 × -500 ×, with sub-micrometer eyepiece and wide angle ● large eyepiece WF10 × / 22, Infinity flat field lens 5 ×, 10 ×, 20 ×, 50 × ● instrument base. Block 300 * 240mm, mechanical stage 250 * 200mm, mobile 100 * 100mm. ● lifting range 120mm, coaxial coarse focusing ≥30mm, trimming 1μm. ● Coaxial epi-illumination, variable aperture and field diaphragm within the polarization switching device ● Optional: Property / eyepiece, darkfield, differential interference, imaging systems, flattening machine, metallographic sample preparation equipment.