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. Differential interference contrast system configuration by refraction optical interferometer to produce three-dimensional objects to be observed so that the relief effect, highlighting the relative hierarchy, more clearly identify the specimen is not visible or difficult to distinguish some of the structural details or defects, DIC contrast the image is clear, interference uniform, strong sense of relief. ● 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.