Hi Clo,

When using the Diffraction Encircled Energy, OpticStudio computes the enclosed energy within your point spread function (PSF) as calculated by either the **Analyze..PSF..FFT PSF** or **Analyse..PSF..Huygens PSF**, depending on wether you have checked the **Use Huygens PSF** checkbox of your Diffraction Encircled Energy analysis.

For the FFT PSF, this is an excerpt from the Help File:

The PSF algorithm exploits the fact that the diffraction PSF is related to the Fourier transform of the complex amplitude of the wavefront in the exit pupil of the optical system

For the Huygens PSF, this is an excerpt from the Help File:

To compute the Huygens PSF, a grid of rays is launched through the optical system, and each ray represents a particular amplitude and phase wavelet. The diffraction intensity at any point on the image surface is the complex sum of all these wavelets, squared.

In short, OpticStudio will either use the actual wavefront of your system at the exit pupil or actual real ray traces through your system. This means that OpticStudio is indeed considering aberrations, even in the case of Diffraction Encircled Energy.

I guess the simple reason behind this behaviour is that it is more accurate than just using the Airy disk. Using those calculations, you get an image of your PSF that truly reflects the performance of your system.

If your two systems have the same NA and wavelength, they’ll have the exact same Airy disk. And it begs the question: why would you want to compare them in the first place if they are the same?

I think your approach with the Diffraction Encircled Energy is sensible, why not continuing in this direction? I might have misunderstood your question, so feel free to correct me or give me more detail about the problem.

Take care,

David