In computer-aided sequential lens design, rays are traced from one surface to the next in the order in which they are listed.  To do this, ZEMAX uses a spreadsheet format called the Lens Data Editor (LDE).

Upon opening ZEMAX, a blank LDE will appear within the main ZEMAX window.  The main ZEMAX window has a large blank area, with a title bar, menu bar, and toolbar at the top.  The LDE is the primary spreadsheet where the majority of the lens data is entered.  Some of the main entries include the following

  Surf: Type the type of surface (Standard, Even Asphere, Diffraction Grating, etc)
  Comment an optional field for typing in surface specific comments
  Radius surface radius of curvature (the inverse of curvature) in lens units
  Thickness the thickness in lens units separating the vertex of the current surface to the vertex of the following surface
  Glass the material type (glass, air, etc.) which separates the current surface and the next surface listed in the LDE
  Semi-Diameter the half-size of the surface in lens units

Main ZEMAX window and LDE

Each row within the LDE represents a single surface.  In sequential ZEMAX, each optical system begins at the object (OBJ) and ends at the image (IMA).  In addition to the object and image planes, one of the surfaces must be defined as the aperture stop (STO).

Data can be entered into the LDE by typing in the required values in the highlighted cell.  The cursor keys or the mouse may move the highlighted bar to whichever column is desired.