3.4 The Focal Length of a Lens3.5 Ray-Tracing; 3.6 Lenses in the Microscope; 3.7 Conjugate Planes; 3.8 The Single Lens Magnifier, or Loupe; 3.9 The Compound Microscope; 3.10 Magnification in the Compound Microscope; 3.11 Useful Magnification; 3.12 Similarities between Different …