Optical testing instruments use optical measurement technology to quickly and precisely measure the size, angle, and flatness of products. From the development of optical inspection instruments to the present, there are optical projectors, tool microscopy, coordinate measuring machines and image measuring instruments. The optical projector uses the imaging principle of the projection light path, enlarges the image of the part according to a specific ratio and projects it on a large circular screen, and then compares it with the part drawing to judge whether the part is qualified. Although there are currently measuring instruments with higher technology and higher accuracy than optical projectors, currently measuring projectors are still one of the optical inspection instruments commonly used in production workshops. The measurement accuracy of the tool microscope is higher than that of the optical projector, because the microscopic imaging optical path of the tool microscope is higher than the projection imaging optical path of the optical projector. The measuring efficiency of the coordinate measuring machine is much higher than that of the tool microscope. During the measurement process, the coordinate measuring machine converts the measurement of various geometric elements of the workpiece into the measurement of the coordinate positions of the points on these geometric elements, including size, shape, relative position, etc. The image measuring instrument is a coordinate measuring machine, which is a further measurement result of the coordinate measuring technology in the measurement field, and the image measuring instrument industry is also born from this.