Danubia 1.25″ K17 Kellner is a 17mm eyepiece for Astro Telescopes which is fully coated and offers a wide angle field of view, so is really useful for locating smaller objects in the night sky. Easy to fit to a telescope with a 1.25″ diameter eyepiece aperture, the Kellner style of eyepiece, is an achromatic one and has a three lens design. It gives excellent eye relief and is a terrific aid to extended night time viewing.