field glasses vs pair of binoculars

field glasses

noun
  • binoculars. 

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 field glasses and pair of binoculars occurred in a corpus of books? (source: Google Ngram Viewer )