Open the file 'Paraxial Equivalent.zmx'. It models the same sytem with just a paraxial lens surface:



Note the following:

• It uses the same field and wavelength as the original design.
• Its entrance pupil diamater is set to the same value as the exit pupil diameter of the original system. In this file the entrance pupil, stop surface and exit pupil are all co-located.
• The focal length of the paraxial lens, and the thickness to the image surface, are both set equal to -1*exit pupil position of the original file. The -1 factor is because the EXPP is measured from the image to the pupil, but the surface thickness is the distance from the pupil to the image, and so need to change sign.
• The system has the same first-order properties as the original system.

The exit pupil of this system is exactly the same size and in the same location as the exit pupil of the original system. In order to add aberrations onto the paraxial lens output, we use a Zernike Standard Phase surface immediately after the paraxial lens. Our goal is to take the Zernike coefficients of the original lens, and add them onto the Zernike surface of the paraxial equivalent lens.