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. SV245 With 8-element multi-coated optics, including aspheric lenses, SVBONY SV245 Universal Zoom Eyepiece delivers stunning sharpness, contrast, and color correction across a wide 63° field of view. Parfocal from 8-16mm, it eliminates the need for constant refocusing. It features 18-17mm eye relief and an adjustable rubber eyecup, perfect for glasses or direct use. Compatible with 1.25" and 2" barrels.