1. it may be that the converter is not in the positioning position, try to switch the converter to the positioning position;2. it may be that the dial of the tube mirror is not in the positioning position. Try to turn the dial of the tube mirror to the positioning position;3. It may be that the brightness of the lighting is insufficient. Try to adjust the brightness of the light source or make the aperture of the light bar larger.4. It may be that the eyepiece is not installed, please install the eyepiece;5 it may be that there is no objective lens. Please install the objective lens.