The Televue 3mm - 6mm Nagler Click-Stop Zoom has a 1.25" barrel size to fit 1.25" focusers, adapters, diagonals or accessories.With 3, 4, 5, and 6mm settings, it's like having four Nagler eyepieces in one!The Televue 3mm - 6mm Nagler Click-Stop Zoom has 10mm of eye relief and a great 50degree apparent field of view.Get every last little bit of magnifying power out of your telescope the atmosphere will permit!The Televue 3mm - 6mm Nagler Click-Stop Zoom features full multi-coating, blackened lens edges, fold-down eyeguard, rubber grip-ring, safety undercut, anti-reflection threads and filter threads.