The SV215 zoom eyepiece is designed to provide the good balance of contrast, comfortable eye relief, and resolution for the critical planetary observer, particularly those with ultra-premium short focal length refractors. Parfocal Design: SV215 zoom eyepiece maintains focus throughout the zoom. You don't have to refocus when you magnify. Click /Stops: Improve the customer's hand feel of variable times adjustment operation. Smooth zoom action with click-stops at 3, 4, 5, 6,7 and 8mm for quick changes to precise preset magnifications. Apparent Field of View: 56°：The field of view will not change with the change of focal length, the process of doubling to give customers a fixed point to pull into the visual enjoyment. SVBONY SV230 super zoom eyepiece provides you with a wide range of magnifications all combined in a single eyepiece. It is convenient to observe planet. *Wide angle eyepiece, expand the view of sight. *Wider coverage, compatible with more brands. *Output images without edge distortion." "Panoramic Wide Angle 57°-72°panoramic wide angle provides you with the ultimate observation comfort" "Aspherical Lens The aspherical lens is designed to eliminate edge distortion, it has resolved the persistent issue of subpar edge image quality associated with wide-angle eyepieces, thereby transcending the visual constraints experienced by users." "Parfocalization Parfocal across the entire zoom range.There is almost no need to refocus when changing magnification.