They can make telescopes, suitable for a variety of applications, including scientific experiments, photography, and optical instruments. Specification Color: Transparent Material: Glass Double Convex Lens 1# Focal Length: 5cm, Diameter:30mm / 1.18" 2# Focal Length: 10cm, Diameter:40mm / 1.57" 3# Focal Length: 10cm, Diameter:50mm / 1.97" Double Concave Lens 1# Focal Length: 5cm, Diameter:30mm / 1.18" 2# Focal Length: 10cm, Diameter:40mm / 1.57" 3# Focal Length: 10cm, Diameter:50mm / 1.97" Packing List: 6 x Glass Lens Advantage Made of quality glass that is durable, scratch resistant, and provides excellent optical performance. Round edges have been polished, it is not easy to hurt your hand when you assemble it. Designed with a double concave shape that let the light diffuse and produces virtual images. The double convex shape of the lens provides a wider field of view, resulting in clearer and sharper images. The lens is accurately measured and has consistent curvature, ensuring consistent performance and results. Instruction Concave Lens: Place the concave side of the lens facing the object from which you want to disperse the light. Adjust the distance between the object and the lens until the desired level of dispersal is achieved. Convex Lens: Once you have determined the focal length, position the lens in front of the light source. The side of the lens that is curved outward should face the object you want to focus the light on. Move the lens back and forth until the image of the object is in focus on the screen or surface. NOTE: Remember to handle the lens with care to avoid scratches or damage to the surface.