To demonstrate the accuracy within the bounds of the model glass, please open the sample file attached on the Summary and References page of this article. 

FILE:  “Accuracy of the Model Glass.ZMX”

The attached file includes two configurations of a single lens, one which uses a model glass and one which uses a glass (N-BK7) already included in the ZEMAX Glass Catalog database.

In configuration 2, the model glass is used to best approximate N-BK7 glass from Schott.  From Schott’s website, http://www.us.schott.com/optics_devices/english/products/flash/abbediagramm_flash.html, we can find the following information about the properties of N-BK7 glass:

 

The highlighted parameters above are typed into the appropriate entries for the model glass in configuration 2:



The Merit Function Editor in the current demonstration file has been constructed to demonstrate the difference in refractive index for various wavelengths between the two configurations.

Wavelengths 1 through 3 are within the visible spectrum.  As you can see, the wavelength differences between the model glass and the actual N-BK7 glass are quite small (<0.0001).  Wavelength 4, on the other hand, is well beyond the visible spectrum, and thus the difference in refractive index becomes much larger (a difference of ~0.008087). 

Small changes in refractive index can lead to significant changes in the refraction of rays, which inherently affect the performance of an optical system.  Even in the presented case, note the slight difference in the paraxial image location (as calculated using a Marginal Ray Height solve) in the two configurations.  Though the index of refraction of wavelength 2 (the primary wavelength) differs only slightly between the two models, the image plane location differs by roughly 0.5 microns.