Aligns the phone lens with the binocular lens for photos and for videos. Reinforced cast aluminum frame keeps a tight grip on the binoculars, while spring loaded phone clamp, also of aluminum holds the smartphone tight. Eyecup width between 24-46mm, which covers the spectrum of optics. Phone widths between 62-104mm will fit (iPhone 5 sans case is too narrow). Folds down to a small size that easily fits in pocket.