SVBONY eyepieces are used to increase magnification to ease viewing Beautifully made with machined housings. The metal body gives you a different metallic feel experience. 62 degree ultra wide field of view. Maximum detail and definition across the entire field of vie;get high definition and a virtually distortion free image.The structure of the optical system. Aspheric eyepiece designed primarily for planetary observation and perfect for deep sky objects. built-in black extinction thread. SVBONY 23mm telescopes eyepiece has black extinction thread, which can reduce the interference of other light, and make the observation effect more better. FMC broadband multiple coating for high light transmission. Equipped with a precision-made standard 1.25-inch lens barrel that is compatible with any telescope that accepts 1.25-inch eyepieces. SV135 fully multi-coated zoom plossl eyepiece zooms to any focal length between 7 mm and 21 mm - pick the better magnification for your subject. As a beginner; SV135 zoom eyepiece is good for starter astronomer! 7mm-21mm linear continuous zoom. Regarding the zoom action; it is stiff enough that you won't accidentally shift focal lengths; but it is also smooth enough that you can rotate it without holding the base of the eyepiece with your other hand. 6-Element 4-Group premium optical with FMC ultra high quality standard coating;It also ensures the transmission of light up to 97% while reducing the loss of light during transmission. 1.25in Diagonal fits telescopes with 1.25in focusers. Accepts standard 1.25” eyepieces, filters, Barlow lenses and other accessories with a 1.25in insert barrel. 90° Viewing Angle. For more comfortable overhead viewing through refractor and Cassegrain type telescopes. Upright Image. Correct upside down and left right reversed image. It will look like trying to read a sign in a mirror. Suitable for space viewing, for there is NO upside down or right side up in space.