adjustable focal length;SV135 7-21mm zoom eyepiece equivalent to multiple eyepieces ;obtain higher magnification with short focal length;It could bring you a better observation experience in a comfortable situation with high-contrast imaging 18mm - 16.3mm comfortable eye relief; especially for eyeglass wearers ;designed primarily for viewing landscapes and astronomical observations of lunar surfaces; planets; nebulae; clusters; and diffuse nebulae fully multi-coated Premium eyepiece with superior edge and center sharpness than normal PLOSSL eyepieces; 6-Element 4-Group premium optical design for superior optical performance Standard 1.25" eyepiece;Equipped with a precision-made standard 1.25-inch lens barrel that is compatible with any telescope that accepts 1.25-inch eyepieces
Eye Relief: 18mm - 16.3mm°
Eye relief seems much more important for glasses wearers, whether you have a poor sight or wear sunglasses on a strongly sunny day. And this eyepiece’s eye relief is 18-16.3mm, comfortable for viewing with or without glasses.
FMC Optics & Edge Blackened
Fully multi-coated optics and that the edge of every glass is blackened ensure high light transmission and reduce stray light for excellent and high-contrast images.
Focal Length: 7mm to 21mm
Zoom eyepiece brings great convenience to visual astronomy that there are no swapping between eyepieces to change magnification and there is no need to break away form your observing to change the focal length. And the 6-Element 4-Group optical design for superior optical performance. PLEASE NOTE: Due to the structure of zoom eyepiece, the internals will produce a slight rattling sound when changing the magnification or shaking.
1.25” Interface & M28.5*0.6 Thread
The eyepiece is threaded for a filter (standard M28*0.6 female thread) and the interface diameter is1.25” for connecting to a telescope for visual celestial astronomy, like moon and high powered terrestrial targets at a broad range of focal lengths.
Field of View: 57-40°
Equipped with a generous 40° to 57° field of view and a non-click stop adjustment mechanism, this eyepiece allows smooth transitioning between focal lengths, ensuring that the observer can find the perfect combination of field of view and magnification that the target object and seeing conditions will allow.
SVBONY SV135 7mm to 21mm 1.25inch Zoom Eyepiece