Opera glasses, also known as theater binoculars or Galilean binoculars, are compact, low-power optical magnification devices, usually used at performance events. Magnification (power) below 5x is usually desired in these circumstances in order to minimize image shake and maintain a large enough field of view. A magnification of 3x is normally recommended. When used at a musical, the opera, the ballet, rock concert, theater, or circus, good opera glasses or pocket-sized compact theater binoculars can provide a front row view. Unlike binoculars, which are a pair of matched, folded terrestrial telescopes, opera glasses use Galilean optics, having a convex objective but a concave eyepiece. This allows the device to produce an upright image with a short length, although with some loss of image quality and angle of view.
