The singlet will be made of N-BK7 glass.  In ZEMAX, this is the material separating the front and back surfaces of the lens.  Enter the glass type separating these two surfaces by simply typing the name of the glass (N-BK7 in this example) in the appropriate cell in the LDE.



ZEMAX automatically recognizes this glass type as one of the many glasses which are compiled into the built-in Glass Catalog.  The Glass Catalog contains all of the necessary information for hundreds of glasses provided by manufacturers around the world.  ZEMAX will automatically look up this glass in its database to determine the index of refraction of the material at each design wavelength.

Once the glass type is entered into the LDE, the lens thickness for the singlet may be typed into the Thickness column for Surface 1.  Since the thickness is the distance along the optical axis to the next surface, this becomes the center thickness of the lens element.  As a starting point, a thickness of 4mm may be applied as it is a reasonable center thickness for an aperture of 25mm.  Type in a value of 4 into the Thickness column for Surface 1.  Note that this parameter will later be set as a variable for optimization.

Similarly, the radius of the first surface and the thickness between the back of the lens and the image need not be pre-determined since they will be set as a variables for optimization.  For the time being, we will leave the Radius of Surface 1 as Infinity and change the Thickness of Surface 2 to 100mm.  Type in the value of 100 into the Thickness column of Surface 2.