About this item Single Eye Observation: Considering its area observation character, it is suggested to observe with one eye. It can't focus when you use a lens with two eyes at the same time Focal Length: The higher the magnification, the shorter the focal length will be. Adjust the focal length from 0.2 to 10.2 inches (0.5-25.9cm) by changing different lenses Replaceable Lens: 8 pairs of lenses with different magnifications (2.5, 4, 6, 8, 10, 15, 20, 25) are included. For larger examination, please refer to 2.5X to 8X magnification Humanized Design: Equipped with LED light, it can help you work in low light conditions. Detachable bracket and headband ensure tight wearing and reduce fatigue Wide Usage: It can be used in mechanical processing, electronic repair, jewelry appraisal, watch repair and miniature engraving, etc.