Tele Vue 3x Barlow Lens (1.25") BLW-3125 B&H Photo Video
What Is A Barlow Lens and How To Use One
Amazon.com : 3X Barlow Lens, 3X Astronomical Telescope Eyepieces Barlow Lens with M42x0.75mm Thread, T Ring Adapter for 24.5mm Astronomical Telescope/Digital Camera : Electronics