field glass vs spotting scope

field glass

noun
  • A small monocular refracting telescope. 

  • A pair of binoculars for observing "in the field". 

  • The larger of the image lenses of an optical device. 

spotting scope

noun
  • A compact high-power monocular telescope optimized for detailed observation of distant objects such as wildlife or the strike of a bullet on a target. 

How often have the words field glass and spotting scope occurred in a corpus of books? (source: Google Ngram Viewer )