Well, they are supposed to be different...there’d be no point in having these multiple features if they all gave the same answer 

It’s really more about the question that each feature is trying to answer. POP gives the response of the system to a Gaussian beam. FFT and Huygens PSFs are, well, Point Spread Functions: the response of a system to a point. The FFT is faster but more approximate than the Huygens, so if they give different results when well-sampled, trust the Huygens result. 

The final difference is that the FFT and Huygens PSFs only consider the diffraction is propagating from the exit pupil to the image. This is an excellent assumption, but POP will account for diffraction effects from any surface. In most imaging systems that’s not important, but it might be, and it’s also why POP has to be much higher sampled in general than the other two methods.

• Mark

Thank you very much!

1. Why do FFT PSFs have many assumptions? 
2. There are many types of PSF cross section, what is the meaning of them all? 
3. Pupil sampling is usually more accurate the more samples are taken, what kind of sampling points are generally used? 
4. Why is the difference between Geometric/FFT/Huygen MTF so big even if the PSFs are the same in the same optical system? 
5. What is the general case of FFT PSF, Huygens PSF will say that it is using scalar diffraction theory, generally refers to the Fraunhofer diffraction theory? 
6. Huygens PSF in ZMX considers full fields, then is FFT PSF also considers the full fields? 
7. Polarization can set in the field, does it represent the polarization of the light source? Is there any relationship between FFT PSF/ Huygens PSF and polarization options? Do you have the relevant theory, equations and reference material recommendations? 

I've been thinking a lot about this recently, but I'm a student and my knowledge is too small, so I'm looking forward to the answers of all the experts who know. Thanks in advance!

Hi Liying,

To learn more about the details and settings of the PSF calculations, I would suggest to take a look at these knowledgebase articles:

What is a Point Spread Function? – Knowledgebase (zemax.com)

What is the difference between the FFT and Huygens PSF? – Knowledgebase (zemax.com)

What does the sampling correspond to in wavefront-based calculations? – Knowledgebase (zemax.com)

More info about the MTF calculations can be found here:

Methods for analyzing MTF in OpticStudio – Knowledgebase (zemax.com)

Finally, regarding the polarization features, please see here:

Investigating OpticStudio’s polarization features – Knowledgebase (zemax.com)

Best,
Csilla

Thank you for your suggestions. In fact, I have read most of the passages that you suggested and maybe I need to enrich the theories about the part that I asked.

Hey Liying,

It would probably help to ask more specific questions. If you’ve read and followed the KB articles, it would be good to focus on the exact questions you need answers to. It would probably also help to start a thread for each distinct question 

• Mark