A theoretical Point Spread Function (PSF) is a PSF numerically computed based on a model of the microscope and known Microscopic Parameters.
Huygens deconvolution can use this theoretical PSF, which - although it is automatically determined in the software - is incorrectly confused with 'Blind Deconvolution'.
Images affected by Spherical Aberration due to a Refractive Index Mismatch are better restored with Huygens Software through the use of depth-dependent PSF's. (That is because Mismatch Distorts Psf). Currently this depth-dependency can be only achieved through theoretical PSF's calculating a different PSF for different Acquisition Depths; Experimental Psfs can not be adapted by now.
Apart from this point, the best PSF is always an Experimental Psf.
When you deconvolve an image in the Huygens Software without providing an experimental PSF, a theoretical one is automatically calculated based on the microscopic parameters of the dataset. Therefore setting these correctly is very important.
With Huygens Professional you can calculate and make an image of a theoretical PSF for any set of microscopic parameters using the "Theor.PSF" button in the taskbar of the Operation Window. Fore more detailed instructions, go to the Visualize Theoretical PSF tutorial page.
You can also do this within the tcl command shell. For example to calculate and display the theoretical PSF of image "a" to thumbnail "psf" you type:
a genpsf -> psf
Huygens Scripting also does it, and it is the engine behind the online PSF calculator.
See also Theo Vs Exp Psf.