eyepiece vs seeable

eyepiece

noun

  • The lens (or combination of lenses) at the eye end of a microscope or telescope by which the image is viewed. 

seeable

noun

  • That which is to be seen. 

adj

  • Able to be seen; visible. 

How often have the words eyepiece and seeable occurred in a corpus of books? (source: Google Ngram Viewer )