Calculation of the EXPD operand

  • 13 September 2021
  • 2 replies

Dear OpticStudio community,

I was wondering whether anybody could comment on the following context.

I’m using a microscope objective model with an NA of 0.95 in air, where the high NA side is located in the object space. The aperture type in the software is defined as object-side NA. Also, ray aiming (real) is on to equidistantly sample the aperture stop.

I’m interested in the diameter of the exit pupil (ExP), because there I want to extract the optical path difference relative to the chief ray with rays that equidistantly sample the exit pupil. For this purpose, I have to remap the rays in the aperture stop so that the condition to sample equidistantly the ExP is fulfilled.

Here I run over the fact that the 2x paraxial ray height at the ExP plane from the merit function editor does not match the operand EXPD.

So my question is how does the software calculate the EXPD operand and why I might get that difference

Thank you very much in advance.


2 replies

Userlevel 5
Badge +3

Hey Alex,

the fact that you need ray-aiming shows that paraxial quantities can’t be relied on. Try tracing a parabasal ray instead. This is a real ray, with very small pupil coordinate, scaled to full pupil.


Hey Mark,

thank you very much for the hint & also your youtube channel. It helped me a lot.

Indeed tracing a real ray at  1% of the pupil height corresponds very close to the half of the EXPD value.

Moreover, what do you think about the procedure I described above to extract the OPD relative to the chief ray  at the ExP when raytracing is on  and remapping the aperture ray trace grid? My purpose is to model the wavefront for an on axis field which could be seen by a Shack-Hartmann sensor behind the microscope objective in an equidistant coordinate system of the ExP.

Again thank you very much.