refracting telescope vs spotting scope

refracting telescope

noun
  • A telescope which produces a magnified image by refracting light through a series of lenses housed in a tube, with a light-gathering objective lens at one end and an eyepiece at the other. 

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 refracting telescope and spotting scope occurred in a corpus of books? (source: Google Ngram Viewer )