Tele Vue 13mm Nagler Type 6 Eyepiece - 1.25" - EN6-13.0About the TeleVue 13mm Nagler Type 6 Eyepiece 1. 25" The 7 element, TeleVue 13mm Nagler Type 6 design is based on the original patented Nagler design. This new 7 element TeleVue Telescope Eyepiece design update for the short focal length Nagler deserves its own designation. Using different exotic materials, coating processes and design ingenuity, Al has massaged more eye relief, contrast, and true field of view into the shorter focal length Naglers,