Features: Provide focal length option of 20mm, 10mm, and 4mm to meet different observation needs, allowing users to have a wide field of view or high magnification. The surface of the lens is treated with an anti reflective film, which can reduce reflection and scattering, provide clear and sharply images, and make observations more accurate and detailed. Made from metal materials, it is durable and has a long lifespans, suitable for long-term observation use. Easy to install: With a 1.25inch standard interfaces, it is suitable for most astronomically telescopes, making installation and replacement easy and quick. Suitable for enthusiasts, astronomy students, amateurs astronomers, and professional astronomers interested in astronomically observation. Specifications: Material: Metal Focal Length: 4mm(0.16inch)/10mm(0.39inch)/20mm(0.79inch) Interfaces Size: Approx. 1.25inch/31.7mm Lenses: Optical Lenses Coating: Full surface coating Package Includes: 1x Astronomy Telescope Eyepiece note: Please allow 1-2cm errors due to manual measurement, make sure that you do not mind before you order. Due to the difference between different monitors, the picture may not reflect the actual color of the item.