Dorr Danubia 1.25-Inch K17 Kellner 17mm Astro Telescope Eyepiece is a quality, coated eyepiece, which gives a wider angled field of view, so is great for locating smaller objects in the night sky. It is easy to fit a telescope with a 1.25" diameter eyepiece aperture. The Kellner style of the eyepiece is an achromatic one and has a three-lens design. It is fine quality material construction to assure durability and performance. It gives excellent eye relief and is a terrific aid to extended night time viewing.