This example shows a case where Ray-aiming must be used. Open the included sample file Ray Aiming sample 2.zip and set the Ray-aiming to “off”.

You will notice that all the rays from the object space, i.e. before surface #4, are aimed at the paraxial entrance pupil. The entrance pupil position in the Prescription Data is in surface #1 coordinate system, hence in this example it is 1.82915 lens unit (mm for this file) right of surface #1.

The semi-diameter of the stop surface is set automatically in the Lens Data Editor to allow real marginal rays from all fields and wavelength to pass the stop. Note that with Ray-aiming off, none of the rays from field #3 can even reach the stop surface, since given the incident angle the rays cannot travel through all surfaces prior to stop; a requirement in sequential ray tracing. 

Before ZEMAX can aim the rays to properly fill the stop, the size of the stop has to be determined first, unless explicitly specified by using “float by stop size” aperture type (for this file, the system aperture type is Entrance Pupil Diameter).  With "Paraxial" Ray-aiming, the size of the stop, to which the rays are aimed at, is determined by the paraxial marginal ray height at the stop surface. To find out this value, even without Ray-aiming, open the Ray Trace Calculation under Analysis > Calculation > Ray Trace, and by clicking Settings in the menu, set the field to 1 and pupil coordinate to Px=0 and Py=1; the on axis marginal ray. Under the paraxial ray trace data, the Y height at the stop is reported as being 0.424799 and under the real ray trace data 0.43225. This difference between the real and paraxial marginal ray height is much larger for field #2 as evident from the ray trace calculation and the 2D layout above.