‘I think I should understand that better,’ Alice said very politely, ‘If I had it written down; but I can’t quite follow it as you say it’.
Alice in Wonderland
Until comparatively recently, the discussion of image formation has relied on one of three models for the behavior of light. The ray model uses a geometrical approach and is satisfactory for describing the basic geometry of the formation of an image by an optical device, but it doesn’t describe the nature of the fine structure of an optical image, nor does it predict the phenomenon of diffraction. The Huygens’ wave model does describe diffraction fairly well, but is difficult to use with gratings that are other than binary, ...