The power of binoculars is described by numbers. The first number describes the magnification power. The second number gives the diameter of the objective lens in millimeters. This is a measure of the light-gathering power of the binoculars. So a 7 x 50 pair of binoculars can magnify things up to seven times and has a 50mm objective lens.
Opera glasses are just binoculars with a simple, cheap lens system and a narrow field of view.
For Thought You can use a pair of binoculars for bird watching, star-gazing, looking at shy animals, spotting ships at see, watching a concert, enjoying a sports game from an awful seat, the list goes on and on. You can use them hiking, camping, boating. A guide that includes over 1,100 deep sky objects you can see with binoculars including globular clusters, double stars, binary star systems, and nebulae. This page was last updated February 24, 1996. Peter Piper Publishing Inc.