opera glasses vs pair of binoculars

opera glasses

noun
  • One or more pairs of small low-powered binoculars for use by members of the audience at a theatrical performance. 

pair of binoculars

noun
  • A hand-held device consisting of a series of lenses and prisms, used to magnify objects so that they can be better seen from a distance, and looked at through both eyes. 

How often have the words opera glasses and pair of binoculars occurred in a corpus of books? (source: Google Ngram Viewer )