When given constraints on an optical design, there are two possible methods of upholding these constraints:

  1. Make the parameters which affect these constraints variables and add boundary constraints into the Merit Function Editor (to be introduced shortly) OR
  2. Use special solves to enforce the constraints, eliminating unnecessary variables.

The latter of these two is far superior.  Though both provide a method of adjusting lens parameters to maintain a specified constraint, boundary constraints can slow down execution of the merit function.
 
There are many different solves available within ZEMAX, each of which has a specific purpose.  However, the performance specifications for this design calls for the use of only one of these solves:  one to set the system F/# to maintain the desired focal length.

To activate a solve dialog, right-mouse-click on the desired cell, or highlight the cell and press “Enter” on the keyboard.  Depending upon which parameter the solve is activated, different solves are available. 

To maintain the system F/#, an F Number solve can be placed on the radius of Surface 2.  The F Number solve adjusts the final optical surface curvature to maintain the system focal length.  Right-mouse-click on the Radius cell for Surface 2 to activate the Curvature solve on surface 2 dialog.  Select F Number from the "Solve Type" pull-down menu and type in a value of 4 into the "F/#" entry below.

F Number solve

Click "OK" to close the solve dialog. 

Once the F Number solve is set, ZEMAX will automatically adjust the radius to maintain the desired F/#.    In other words, anytime a lens parameter is altered, the solve will be automatically re-calculated.  The letter "F" next to the radius is indicative of the F Number solve in place.

F Number Solve in LDE