If a glass or material you wish to use in your design does not currently exist in the ZEMAX Glass Catalog, there are various methods available to create this glass in ZEMAX.  One of these methods includes what is called a model glass.  Basically, the model glass is used to idealize a glass by describing the dispersion in the visible wavelength region via a few input parameters.

The model glass is entered into ZEMAX as a solve type via the "Glass" column in the Lens Data Editor (LDE).  To activate the glass solve dialog, right mouse click on the appropriate cell, or position the cursor over the desired Glass cell and press the "Enter" key on your keyboard.

Of the available glass solves, select Model from the available pull-down menu.



The model glass supports three different parameters: Index N_d, Abbe V_d, and Dpgf (DP_g,F), each of which may be used to approximate the refractive properties of your glass (we will discuss this approximation in more detail in the latter pages of this article).  Notice that each of these parameters support a "Vary" checkbox.  By checking this box, the desired parameters may be used as variables in optimization.  ZEMAX can optimize these parameters while constraining the parameter values or the computed index values to be similar to available glasses.  The details of this optimization method are not covered in this article, but you may refer to the "Optimizing glass selection" of Chapter 14 in the ZEMAX User's Guide for more information.

It is important to note that model glasses are an approximation, and there are some subtleties which you should be aware of prior to using the model glass feature in ZEMAX, including:

• what definitions ZEMAX uses to approximate the model glass
• how accurate these approximations really are
• when and when not to use the model glass